Mark test_send_tas_to_celery_hang as quarantined (#16169)

The test_send_tasks_to_celery_hang hangs on self-hosted runners more
often than not.

It's been introduced in #15989 and while the test does not usually hang
on regular GitHub runners, or in case of running it locally (I could not
make it fail), it does hang almost always when run on self-hosted
runners.

Marking it as quarantined for now.

Issue #16168 created to keep track of it.

tests/executors/test_celery_executor.py

@@ -522,6 +522,7 @@ def register_signals():
     signal.signal(signal.SIGUSR2, orig_sigusr2)
 
 
+@pytest.mark.quarantined
 def test_send_tasks_to_celery_hang(register_signals):  # pylint: disable=unused-argument
     """
     Test that celery_executor does not hang after many runs.