repeating calendar event updates with new excluded occurrences don't get properly sent to attendees

[ganthern]

Bug in web app

Describe the bug
repeating event updates where the organizer cancels an occurrence don't get propagated to invitees.

To Reproduce
steps to reproduce the behavior:

1. create a weekly repeating event with account O with an attendee A
2. accept the invite on account A
3. delete a single occurrence on account O, make sure the update gets sent
4. see that the update is applied on account A, but the deleted occurrence is still there. the ICS file also doesn't include the exclusion.
5. as a bonus, change the event title and send an update - this update fixes the issue since other than the notification, everything works.

Expected Behaviour
the occurrence should be removed in the first update mail

Additional context
the culprits are these lines (note the comments):

tutanota/src/calendar-app/calendar/gui/eventeditor-model/CalendarEventModelStrategy.ts

Line 221 in fbc4209

recurrenceIds.push(existingInstance.startTime)

tutanota/src/calendar-app/calendar/gui/eventeditor-model/CalendarNotificationModel.ts

Line 50 in fbc4209

const filteredExclusions = originalExclusions.filter(({ date }) => !recurrenceTimes.includes(date.getTime()))

the event that's being deleted should not be added to the recurrenceIds since it's not going to occcur.

commit ref: bbf68fb