fix strictGenericNarrowing causing false positive reportUnnecessaryIsInstance errors when narrowing Callable

[DetachHead]

fixes #905

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

sympy (https://github.com/sympy/sympy)
-     Type of "rootof" is "(f: Unknown, x: Unknown, index: Unknown | None = None, radicals: bool = True, expand: bool = True) -> (Unknown | One | NegativeOne | Zero | Integer | Rational | NaN | ComplexInfinity | Half | Infinity | NegativeInfinity | Float | _NotImplementedType | Expr)" (reportUnknownVariableType)
+     Type of "rootof" is "(f: Unknown, x: Unknown, index: Unknown | None = None, radicals: bool = True, expand: bool = True) -> (Unknown | One | NegativeOne | Zero | Integer | Rational | NaN | ComplexInfinity | Half | Expr)" (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_inequalities.py:134:9 - warning: Type of "inf" is partially unknown
+     Type of "inf" is "One | NegativeOne | Zero | Integer | Rational | NaN | ComplexInfinity | Half | Unknown" (reportUnknownVariableType)
-     Type of "r" is "Unknown | One | NegativeOne | Zero | Integer | Rational | NaN | ComplexInfinity | Half | Infinity | NegativeInfinity | Float | _NotImplementedType | Expr" (reportUnknownVariableType)
+     Type of "r" is "Unknown | One | NegativeOne | Zero | Integer | Rational | NaN | ComplexInfinity | Half | Expr" (reportUnknownVariableType)
-     Type of "factor" is "(f: Unknown, ..., deep: bool = False) -> (Unknown | Add | Order | Mul)" (reportUnknownVariableType)
+     Type of "factor" is "(f: Unknown, ..., deep: bool = False) -> (Unknown | Add | Order | Mul | Expr)" (reportUnknownVariableType)
-   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_recurr.py:116:5 - warning: Type of "h" is partially unknown
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_recurr.py:116:5 - warning: Type of "h" is unknown (reportUnknownVariableType)
-     Type of "h" is "Any | Unknown" (reportUnknownVariableType)
-   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:104:9 - warning: Return type, "tuple[int, list[_NotImplementedType | Unknown | Any | bool], Any]", is partially unknown (reportUnknownParameterType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:104:9 - warning: Return type, "tuple[int, list[_NotImplementedType | Unknown | Any], Any]", is partially unknown (reportUnknownParameterType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:105:13 - warning: Return type, "Integer | Unknown | NaN | Expr | One | NegativeOne | Zero | Rational | ComplexInfinity | Half", is partially unknown (reportUnknownParameterType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:109:20 - warning: Return type, "Unknown | NaN | Expr | One | NegativeOne | Zero | Integer | Rational | ComplexInfinity | Half", is partially unknown (reportUnknownVariableType)
-     Type of "constraints" is "list[_NotImplementedType | Unknown | Any | bool]" (reportUnknownVariableType)
+     Type of "constraints" is "list[_NotImplementedType | Unknown | Any]" (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:111:29 - warning: Argument type is partially unknown
+     Argument corresponds to parameter "iterable" in function "sum"
+     Argument type is "Generator[Any | Unknown, None, None]" (reportUnknownArgumentType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:113:25 - warning: Argument type is partially unknown
+     Argument corresponds to parameter "iterable" in function "sum"
+     Argument type is "Generator[Any | Unknown, None, None]" (reportUnknownArgumentType)
-   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:114:16 - warning: Return type, "tuple[int, list[_NotImplementedType | Unknown | Any | bool], Any]", is partially unknown (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:114:16 - warning: Return type, "tuple[int, list[_NotImplementedType | Unknown | Any], Any]", is partially unknown (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:181:5 - warning: Type of "ans" is partially unknown
+     Type of "ans" is "tuple[Unknown, list[int | Unknown]]" (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:221:9 - warning: Type of "ans" is partially unknown
+     Type of "ans" is "tuple[Unknown, list[int | Unknown]]" (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:222:48 - warning: Argument type is partially unknown
+     Argument corresponds to parameter "iterable" in function "__init__"
+     Argument type is "zip[tuple[Any, int | Unknown]]" (reportUnknownArgumentType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:222:55 - warning: Argument type is partially unknown
+     Argument corresponds to parameter "iter2" in function "__new__"
+     Argument type is "list[int | Unknown]" (reportUnknownArgumentType)
-     Type of "ans" is "tuple[Expr | Rational | NaN | ComplexInfinity | One | NegativeOne | Zero | Integer | Half | Infinity | NegativeInfinity | Float | Number | Unknown | Order | int, list[int | ComplexInfinity | Rational | NaN | One | NegativeOne | Zero | Integer | Half | Infinity | NegativeInfinity | Float | _NotImplementedType | Expr]]" (reportUnknownVariableType)
+     Type of "ans" is "tuple[Unknown, list[int | Unknown]]" (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:230:53 - warning: Argument type is partially unknown
+     Argument corresponds to parameter "iterable" in function "__init__"
+     Argument type is "zip[tuple[Any, int | Unknown]]" (reportUnknownArgumentType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:230:60 - warning: Argument type is partially unknown
+     Argument corresponds to parameter "iter2" in function "__new__"
+     Argument type is "list[int | Unknown]" (reportUnknownArgumentType)
-     Type of "ans" is "tuple[Expr | Rational | NaN | ComplexInfinity | One | NegativeOne | Zero | Integer | Half | Infinity | NegativeInfinity | Float | Number | Unknown | Order | int, list[int | ComplexInfinity | Rational | NaN | One | NegativeOne | Zero | Integer | Half | Infinity | NegativeInfinity | Float | _NotImplementedType | Expr]]" (reportUnknownVariableType)
+     Type of "ans" is "tuple[Unknown, list[int | Unknown]]" (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:236:53 - warning: Argument type is partially unknown
+     Argument corresponds to parameter "iterable" in function "__init__"
+     Argument type is "zip[tuple[Any, int | Unknown]]" (reportUnknownArgumentType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_simplex.py:236:60 - warning: Argument type is partially unknown
+     Argument corresponds to parameter "iter2" in function "__new__"
+     Argument type is "list[int | Unknown]" (reportUnknownArgumentType)
-     Type of "n" is "Unknown | Overload[(n: int = 15, subs: dict[Basic, Basic | float] | None = None, maxn: int = 100, chop: bool = False, strict: bool = False, quad: str | None = None, verbose: bool = False) -> Expr, (n: int = 15, subs: dict[Basic, Basic | float] | None = None, maxn: int = 100, chop: bool = False, strict: bool = False, quad: str | None = None, verbose: bool = False) -> Basic] | Any" (reportUnknownMemberType)
+     Type of "n" is "Unknown | Overload[(n: int = 15, subs: dict[Basic, Basic | float] | None = None, maxn: int = 100, chop: bool = False, strict: bool = False, quad: str | None = None, verbose: bool = False) -> Expr, (n: int = 15, subs: dict[Basic, Basic | float] | None = None, maxn: int = 100, chop: bool = False, strict: bool = False, quad: str | None = None, verbose: bool = False) -> Basic]" (reportUnknownMemberType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:479:5 - warning: Type of "sol" is partially unknown
+     Type of "sol" is "dict[Any, Unknown]" (reportUnknownVariableType)
-   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:1385:13 - warning: Argument type is Any
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:1385:13 - warning: Argument type is unknown
-     Argument corresponds to parameter "lhs" in function "__new__" (reportAny)
+     Argument corresponds to parameter "lhs" in function "__new__" (reportUnknownArgumentType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:1385:41 - warning: Argument type is unknown
+     Argument corresponds to parameter "rhs" in function "__new__" (reportUnknownArgumentType)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:1563:5 - warning: Type of "answer" is partially unknown
+     Type of "answer" is "list[dict[Any, int] | dict[Any, int | Any | Unknown]]" (reportUnknownVariableType)
-   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:2498:23 - warning: Argument type is Any
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:2498:23 - warning: Argument type is unknown
-     Argument corresponds to parameter "args" in function "__new__" (reportAny)
+     Argument corresponds to parameter "args" in function "__new__" (reportUnknownArgumentType)
-   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:2507:5 - warning: Type of "eq" is Any (reportAny)
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:2507:5 - warning: Type of "eq" is unknown (reportUnknownVariableType)
-   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:2508:18 - warning: Argument type is Any
+   /tmp/mypy_primer/projects/sympy/sympy/solvers/tests/test_solvers.py:2508:18 - warning: Argument type is unknown
-     Argument corresponds to parameter "eq" in function "unrad" (reportAny)
+     Argument corresponds to parameter "eq" in function "unrad" (reportUnknownArgumentType)

... (truncated 5146 lines) ...

mongo-python-driver (https://github.com/mongodb/mongo-python-driver)
-   /tmp/mypy_primer/projects/mongo-python-driver/tools/convert_test_to_async.py:85:21 - warning: Unnecessary isinstance call; "(...) -> object" is never an instance of "classmethod[Unknown, ..., object]" (reportUnnecessaryIsInstance)
+   /tmp/mypy_primer/projects/mongo-python-driver/tools/convert_test_to_async.py:85:21 - warning: Unnecessary isinstance call; "(...) -> object" is never an instance of "classmethod[Unknown, ..., Unknown]" (reportUnnecessaryIsInstance)

asynq (https://github.com/quora/asynq): 196.68x slower (0.1s -> 12.5s in a single noisy sample)

kopf (https://github.com/nolar/kopf)
-   /tmp/mypy_primer/projects/kopf/kopf/_core/engines/admission.py:266:10 - warning: Unnecessary isinstance call; "WebhookServerProtocol" is never an instance of "AbstractAsyncContextManager[object, bool | None]" (reportUnnecessaryIsInstance)
+   /tmp/mypy_primer/projects/kopf/kopf/_core/engines/admission.py:266:10 - warning: Unnecessary isinstance call; "WebhookServerProtocol" is never an instance of "AbstractAsyncContextManager[Unknown, Unknown]" (reportUnnecessaryIsInstance)

vision (https://github.com/pytorch/vision): 1.59x slower (39.8s -> 63.3s in a single noisy sample)