Fix stubtest tests with typing-extensions>=4.6.0 (#15294)

`teststubtest.py` is currently failing on `master` due to changes that
were made to `typing_extensions.Protocol` in typing_extensions v4.6.0:
https://github.com/python/mypy/actions/runs/5056186170/jobs/9073337924.
This PR fixes the failures.

No need to bump the pinned version of `typing_extensions` in CI, as the
tests will continue to pass if `typing_extensions<4.6.0` is installed.

Author: AlexWaygood

mypy/stubtest.py

@@ -1393,6 +1393,9 @@ def verify_typealias(
         "__dataclass_fields__",  # Generated by dataclasses
         "__dataclass_params__",  # Generated by dataclasses
         "__doc__",  # mypy's semanal for namedtuples assumes this is str, not Optional[str]
+        # Added to all protocol classes on 3.12+ (or if using typing_extensions.Protocol)
+        "__protocol_attrs__",
+        "__callable_proto_members_only__",
         # typing implementation details, consider removing some of these:
         "__parameters__",
         "__origin__",