Add @type_check_only to stub-only private classes in various third-party stubs (#15535)

stubs/docutils/docutils/__init__.pyi

@@ -1,4 +1,4 @@
-from typing import Any, ClassVar, Final, NamedTuple
+from typing import Any, ClassVar, Final, NamedTuple, type_check_only
 from typing_extensions import Self
 
 from docutils.transforms import Transform
@@ -6,6 +6,7 @@ from docutils.transforms import Transform
 __docformat__: Final = "reStructuredText"
 __version__: Final[str]
 
+@type_check_only
 class _VersionInfo(NamedTuple):
     major: int
     minor: int