Read timezone for Crons monitors from `celery_schedule` if existing #3951

Job	Run time
pure_eval, python 3.5, ubuntu-20.04	1m 4s
pure_eval, python 3.6, ubuntu-20.04	50s
pure_eval, python 3.7, ubuntu-20.04	50s
pure_eval, python 3.8, ubuntu-20.04	37s
pure_eval, python 3.9, ubuntu-20.04	40s
pure_eval, python 3.10, ubuntu-20.04	43s
pure_eval, python 3.11, ubuntu-20.04	55s
pure_eval, python 3.12, ubuntu-20.04	1m 22s
All pure_eval tests passed or skipped	1s
	7m 2s

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