Update _asyncio to 3.14 (#14165)

Author: sobolevn

stdlib/@tests/stubtest_allowlists/py314.txt

@@ -2,7 +2,6 @@
 # TODO: New errors in Python 3.14 that need to be fixed or moved below
 # ====================================================================
 
-_asyncio.all_tasks
 asyncio.eager_task_factory
 asyncio.tasks.eager_task_factory
 compression.gzip.GzipFile.readinto

stdlib/_asyncio.pyi

@@ -107,3 +107,4 @@ if sys.version_info >= (3, 12):
 if sys.version_info >= (3, 14):
     def future_discard_from_awaited_by(future: Future[Any], waiter: Future[Any], /) -> None: ...
     def future_add_to_awaited_by(future: Future[Any], waiter: Future[Any], /) -> None: ...
+    def all_tasks(loop: AbstractEventLoop | None = None) -> set[Task[Any]]: ...