Generic class with broken `__eq__` cannot be specialized

Bug report

Bug description:

This test case currently fails:

    def test_buggy_eq(self):
        class BrokenEq(abc.ABCMeta):
            def __eq__(self, other):
                raise TypeError("I'm broken")

        class G(Generic[T], metaclass=BrokenEq):
            pass

        alias = G[int]
        self.assertIs(get_origin(alias), G)
        self.assertEqual(get_args(alias), (int,))

See python/typing_extensions#422 for a real-world example.

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-119973