fix: config list subscript type unsoundness

[Peefy]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

• fix: config list subscript type unsoundness

Before this PR, the following code will get an unexpected type error, which is because the a[0] += [1, 2, 3] has beed inferred with wrong types.

config: {str:[int]} = {
    a += [0, 1, 2]
    a[0] += [1, 2, 3]
}

[coveralls]

Pull Request Test Coverage Report for Build 10494194365

Details

• 0 of 23 (0.0%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 70.914%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
kclvm/sema/src/resolver/config.rs	0	10	0.0%
kclvm/ast/src/ast.rs	0	13	0.0%

Files with Coverage Reduction	New Missed Lines	%
kclvm/sema/src/resolver/config.rs	1	81.8%

Totals
Change from base Build 10486567571:	-0.02%
Covered Lines:	51504
Relevant Lines:	72629

---

💛 - Coveralls

[He1pa]

LGTM