fix test cases like

... prepare the test, create a table or a user
create event ... on schedule every 1 second ... do something ...
... verify that something was done
... cleanup drop event, table or user

here the event scheduler can manage to start the worker for the
second execution of the event, then cleanup happens
and the worker realizes that it cannot change the security context
(as the user is dropped) or cannot insert (as the table is dropped).

followup for 279b0db8 (that removed suppression of /Event Schedule/)