Crash on generic class inside a function with a forward-reference bound

[jelle-openai]

This crashes mypy:

from typing import Generic, TypeVar

def test() -> None:
    T = TypeVar("T", bound="Model")

    class Query(Generic[T]):
        def filter(self, value: T) -> None:
            raise NotImplementedError

    class Model:
        pass

mypy (both 2.1.0 and current master) crashes on this with:

AssertionError: Must not defer during final iteration

Necessary pieces, from reduction:

• The definitions need to be inside a function.
• The TypeVar needs a forward-ref bound to a later local class: bound="Model".
• The local generic class needs to use that T in a method signature.

Similar issues: #12112, #13678, #18579.