Mypy dislikes bound TypeVar in Enum intermediate subclass

Mypy fails to recognise that values on an Enum class that do not appear at run-time should not count as "existing members". If T is moved out of the class definition in the following example, there is no error:

from enum import Enum
from typing import TYPE_CHECKING, TypeVar

class IntermediateEnumBase(Enum):
    if TYPE_CHECKING:
        T = TypeVar("T", bound="IntermediateEnumBase")

    @classmethod
    def _missing_(self: type[T], key: Any) -> T: ...

class FinalEnum(IntermediateEnumBase): ...  # error: Cannot extend enum with existing members: "IntermediateEnumBase"
    ...

This is affecting behave_utils.behave.PatternEnum