Read timezone for Crons monitors from `celery_schedule` if existing #3963

Job	Run time
rq, python 2.7, ubuntu-20.04	6m 58s
rq, python 3.5, ubuntu-20.04	4m 54s
rq, python 3.6, ubuntu-20.04	6m 8s
rq, python 3.7, ubuntu-20.04	2m 44s
rq, python 3.8, ubuntu-20.04	3m 27s
rq, python 3.9, ubuntu-20.04	2m 50s
rq, python 3.10, ubuntu-20.04	57s
rq, python 3.11, ubuntu-20.04	1m 31s
rq, python 3.12, ubuntu-20.04	1m 37s
All rq tests passed or skipped	1s
	31m 7s

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