Fix trailing error with tests. (#901)

<img width="1331" alt="image"
src="https://github.com/lilacai/lilac/assets/1100749/cff378ad-d8df-46e1-8d9c-4d18b485776e">

lilac/tasks_test.py

@@ -4,8 +4,9 @@
 from .tasks import TaskManager
 
 
-async def test_task_manager_outside_event_loop() -> None:
+def test_task_manager_outside_event_loop() -> None:
   # Make sure we can make a default TaskManager from outside a running loop.
   task_manager = TaskManager()
   assert task_manager is not None
-  await task_manager.stop()
+  task_manager._dask_client.shutdown()
+  task_manager._dask_client.close()