Make __replace__ stop interfering with variance inference

Typing
10

I think this is reasonable in most cases. But there are some situations where covariant inheritance is perfectly sound, for example:

@dataclass(frozen=True)
class Base[T: complex]:
    x: T

    def method(self) -> T:
        return self.x

    # def __replace__[T2: complex](self, x: T2) -> Base[T2]: ...

class Child1[T: complex](Base[T]):
    def method(self) -> T:
        return self.x + 1

    # @override
    # def __replace__[T2: complex](self, x: T2) -> Child1[T2]: ...

class Child2(Base[complex]):
    def method(self) -> T:
        return self.x + 1

    # @override
    # def __replace__(self, x: complex) -> Child2: ...

If we assume that no other subclasses exist (i.e. they’re @sealed), then T@Base and T@Child1 can be covariant without violating LSP.