test_k8s/dumps_monitor: ensure a single monitor DAG is running at any given time
This will avoid the 409 errors we've been seeing at the creation of the monitor pods, and ensure we're not hitting potential concurrency/race condution issues with the monitor script itself.
Signed-off-by: Balthazar Rouberol brouberol@wikimedia.org Bug: T390067
Closes T390067