Read timezone for Crons monitors from `celery_schedule` if existing #3961

Job	Run time
starlette, python 3.7, ubuntu-20.04	2m 40s
starlette, python 3.8, ubuntu-20.04	2m 41s
starlette, python 3.9, ubuntu-20.04	2m 5s
starlette, python 3.10, ubuntu-20.04	1m 53s
starlette, python 3.11, ubuntu-20.04	2m 24s
starlette, python 3.12, ubuntu-20.04	2m 29s
All starlette tests passed or skipped	1s
	14m 13s

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