Unbound type variable false positive with six.with_metaclass

[JukkaL]

This code generates a false positive:

import six
import abc
from typing import TypeVar, Generic

T = TypeVar("T")

class C(six.with_metaclass(abc.ABCMeta, Generic[T])):
    pass

class D(six.with_metaclass(abc.ABCMeta, C[T])):  # Type variable "t.T" is unbound
    pass

This is a regression from 0.991 introduced here:

• Support ParamSpec variables in type aliases #14159

@ilevkivskyi Do you have time to look at this? This is a blocker for the 1.0 release.

[ilevkivskyi]

Here is the fix #14478.