Add @type_check_only to stub-only private classes in stdlib (#14512)

stdlib/unittest/case.pyi

@@ -7,7 +7,7 @@ from collections.abc import Callable, Container, Iterable, Mapping, Sequence, Se
 from contextlib import AbstractContextManager
 from re import Pattern
 from types import GenericAlias, TracebackType
-from typing import Any, AnyStr, Final, Generic, NoReturn, Protocol, SupportsAbs, SupportsRound, TypeVar, overload
+from typing import Any, AnyStr, Final, Generic, NoReturn, Protocol, SupportsAbs, SupportsRound, TypeVar, overload, type_check_only
 from typing_extensions import Never, ParamSpec, Self
 from unittest._log import _AssertLogsContext, _LoggingWatcher
 from warnings import WarningMessage
@@ -56,6 +56,7 @@ def skipUnless(condition: object, reason: str) -> Callable[[_FT], _FT]: ...
 class SkipTest(Exception):
     def __init__(self, reason: str) -> None: ...
 
+@type_check_only
 class _SupportsAbsAndDunderGE(SupportsDunderGE[Any], SupportsAbs[Any], Protocol): ...
 
 class TestCase: