This recurrence rule does not generate any valid instances

[mkrecek234]

I have an event created with Apple Calendar on a CalDAV server with this RRULE:
RRULE:FREQ=YEARLY;UNTIL=20230430;BYMONTH=4;BYDAY=SU,SA;BYSETPOS=-1

When saving this to a sabre CalDAV server, I get this error message:
`<s:message>This recurrence rule does not generate any valid instances</s:message>

Event though it looks similar like the issue #1455 the issue is created separately at another stage of editing that event.
Again this is created by Calendar.app, sabreDAV should not throw an exception.

P.S. Do not get any error adding/changing such entry on other CalDAV servers like used in SOgo etc.