fix: fix 3.7 build (#250)

pyproject.toml

@@ -200,6 +200,11 @@ ignore_errors = true
 module = ["wrapt", "msgspec"]
 ignore_missing_imports = true
 
+# remove when dropping python 3.7
+[[tool.mypy.overrides]]
+module = ["psygnal._signal"]
+warn_unused_ignores = false
+
 # https://coverage.readthedocs.io/en/6.4/config.html
 [tool.coverage.report]
 exclude_lines = [

src/psygnal/_signal.py

@@ -492,7 +492,9 @@ def _wrapper(
                         extra = f"- Slot types {slot_sig} do not match types in signal."
                         self._raise_connection_error(slot, extra)
 
-                cb = weak_callback(
+                # this type ignore is only needed to build mypyc on pythong 3.7
+                # can be removed when we drop support for 3.7
+                cb = weak_callback(  # type: ignore
                     slot,
                     max_args=max_args,
                     finalize=self._try_discard,