Having __slots__ in a class causes invariance

[CrowdingFaun624]

When defining a class, its type variables become invariant whenever attributes involving it are in __slots__. This is demonstrated by my examples:

class A[T](): # `T` says it is covariant

    def __init__(self, arg: T) -> None:
        self.arg: Final[T] = arg

class B[T](): # `T` says it is invariant

    __slots__ = ("arg",)

    def __init__(self, arg: T) -> None:
        self.arg: Final[T] = arg

I can't think of a reason for why this would be. arg is immutable whether it is in __slots__ or not, so it should always be covariant. This is pretty annoying for my code, since I like using __slots__.

[jorenham]

This looks like a bug to me.