_asyncio._get_running_loop can return None (#15837)

Author: jonathandung

stdlib/_asyncio.pyi

@@ -99,7 +99,7 @@ class Task(Future[_T_co]):  # type: ignore[type-var]  # pyright: ignore[reportIn
 def get_event_loop() -> AbstractEventLoop: ...
 def get_running_loop() -> AbstractEventLoop: ...
 def _set_running_loop(loop: AbstractEventLoop | None, /) -> None: ...
-def _get_running_loop() -> AbstractEventLoop: ...
+def _get_running_loop() -> AbstractEventLoop | None: ...
 def _register_task(task: Task[Any]) -> None: ...
 def _unregister_task(task: Task[Any]) -> None: ...
 def _enter_task(loop: AbstractEventLoop, task: Task[Any]) -> None: ...