Type hint for check_multiprocess_shutdown_event is confusing for mypy

[doc-sheet]

Hi! For now type hint for shutdown_event is multiprocessing.synchronize.Event

I guess it should be threading.Event instead: simple way to create and pass such event is multiprocessing.Manager().Event() and that's just a threading.Event clone.

references:

1. multiprocessing.managers.SyncManager.Event
2. multiprocessing.Event