Add @type_check_only to various typeshed-only procotols in stdlib (#14465)

Mark various typeshed-only protocols as `@type_check_only` in stdlib

stdlib/cgi.pyi

@@ -3,7 +3,7 @@ from builtins import list as _list, type as _type
 from collections.abc import Iterable, Iterator, Mapping
 from email.message import Message
 from types import TracebackType
-from typing import IO, Any, Protocol
+from typing import IO, Any, Protocol, type_check_only
 from typing_extensions import Self
 
 __all__ = [
@@ -31,7 +31,7 @@ def parse(
 def parse_multipart(
     fp: IO[Any], pdict: SupportsGetItem[str, bytes], encoding: str = "utf-8", errors: str = "replace", separator: str = "&"
 ) -> dict[str, list[Any]]: ...
-
+@type_check_only
 class _Environ(Protocol):
     def __getitem__(self, k: str, /) -> str: ...
     def keys(self) -> Iterable[str]: ...