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

Job	Run time
httpx, python 3.6, ubuntu-20.04	3m 52s
httpx, python 3.7, ubuntu-20.04	2m 47s
httpx, python 3.8, ubuntu-20.04	2m 41s
httpx, python 3.9, ubuntu-20.04	4m 0s
httpx, python 3.10, ubuntu-20.04	2m 5s
httpx, python 3.11, ubuntu-20.04	1m 44s
httpx, python 3.12, ubuntu-20.04	1m 19s
All httpx tests passed or skipped	1s
	18m 29s

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