[3.13] gh-128552: fix refcycles in eager task creation (#128553) (#128585)

gh-128552: fix refcycles in eager task creation (#128553)

(cherry picked from commit 61b9811ac6)

Lib/asyncio/taskgroups.py

@@ -205,7 +205,12 @@ class TaskGroup:
         else:
             self._tasks.add(task)
             task.add_done_callback(self._on_task_done)
-        return task
+        try:
+            return task
+        finally:
+            # gh-128552: prevent a refcycle of
+            # task.exception().__traceback__->TaskGroup.create_task->task
+            del task
 
     # Since Python 3.8 Tasks propagate all exceptions correctly,
     # except for KeyboardInterrupt and SystemExit which are