Create background tasks on application's loop

Author: joouha

src/prompt_toolkit/application/application.py

@@ -1077,7 +1077,8 @@ def create_background_task(
 
         This is not threadsafe.
         """
-        task: asyncio.Task[None] = get_event_loop().create_task(coroutine)
+        loop = self.loop or get_event_loop()
+        task: asyncio.Task[None] = loop.create_task(coroutine)
         self._background_tasks.add(task)
 
         task.add_done_callback(self._on_background_task_done)