Class B_with_slots

Lib/test/test_descr.py:4250–4251

        B_with_dict_weakref.__bases__ = (object,)

        class B_with_slots:
            __slots__ = ('x',)
        b = B_with_slots()
        with self.assertRaisesRegex(TypeError, 'layout differs'):
            B_with_slots.__bases__ = (A_with_dict_weakref,)