Add context manager for contextvars.Token (3.14) (#13997)

stdlib/_contextvars.pyi

@@ -1,5 +1,6 @@
+import sys
 from collections.abc import Callable, Iterator, Mapping
-from types import GenericAlias
+from types import GenericAlias, TracebackType
 from typing import Any, ClassVar, Generic, TypeVar, final, overload
 from typing_extensions import ParamSpec, Self
 
@@ -35,6 +36,11 @@ class Token(Generic[_T]):
     MISSING: ClassVar[object]
     __hash__: ClassVar[None]  # type: ignore[assignment]
     def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
+    if sys.version_info >= (3, 14):
+        def __enter__(self) -> Self: ...
+        def __exit__(
+            self, exc_type: type[BaseException] | None, exc_value: BaseException | None, traceback: TracebackType | None
+        ) -> None: ...
 
 def copy_context() -> Context: ...