Callable[..., T] causes false positive in overload checks

This example:

@overload
def deco(f: Callable[[], int]) -> Callable[[], str]: ...
@overload
def deco(f: Callable[..., int]) -> Callable[..., str]: ...
def deco(f):
    pass

causes

Overloaded function signature 2 will never be matched: signature 1's parameter type(s) are the same or broader

But it should be allowed (the same way we allow various last overloads with Any types).

cc @Michael0x2a