Fix bug in constraints solver regarding ParamSpec upper bounds

[AlexWaygood]

Description

Fixes#12930.

Currently, mypy erroneously emits two errors on this snippet:

fromtyping_extensionsimportParamSpecfromtypingimportCallable, TypeVar, Iterator, Iterable, TupleP=ParamSpec("P") T=TypeVar("T") defenumerate(x: Iterable[T]) ->Iterator[Tuple[int, T]]: ... deffoo(func: Callable[P, T]) ->Callable[P, T]: def_inner(*args: P.args, **kwargs: P.kwargs) ->T: y=enumerate(args) # E: Need type annotation for "y" # E: Argument 1 to "enumerate" has incompatible type "P.args"; expected "Iterable[<nothing>]"returnfunc(*args, **kwargs) return_inner

This is because of a bug in constraints.py: ParamSpecArgs and ParamSpecKwargs have upper bounds following #12668 (tuple[object, ...] and dict[str, object] respectively), but the constraints solver isn't currently aware of that fact. This PR fixes that bug.

Test Plan

I added a test to one of the existing test cases.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉