[3.13] gh-156662: Note that TaskGroup.create_task() raises RuntimeError (GH-156663) (#157315)

gh-156662: Note that TaskGroup.create_task() raises RuntimeError (GH-156663)
(cherry picked from commit 26d9b25)

Co-authored-by: Timofei Ivankov <128279579+deadlovelll@users.noreply.github.com>

Author: miss-islington

Doc/library/asyncio-task.rst

@@ -347,7 +347,7 @@ and reliable way to wait for all tasks in the group to finish.
       The signature matches that of :func:`asyncio.create_task`.
       If the task group is inactive (e.g. not yet entered,
       already finished, or in the process of shutting down),
-      we will close the given ``coro``.
+      we will close the given ``coro`` and raise :exc:`RuntimeError`.
 
       .. versionchanged:: 3.13