Fix class objects falling back to metaclass for callback protocol

[ilevkivskyi]

Fixes #10482

This is not very principled, but should work except people will want to explicitly check some metaclass __call__.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[JukkaL]

I think that this is a reasonable fix, since we don't properly support metaclass __call__ methods anyway. Callable protocols seem like a much more common use case.