[FIX] calendar,google_calendar: exclusions not propagating

Activate Google Synchronization, create on GC a recurrent event,
synchronize OE, then delete an event of the recursion on GC, sync again
on OE.

The event will be deleted from GC but not from OE after sync.

The exclusion on OE is not correctly working in that particular case,
fixing require also to "suppress" the attendee to avoid that just
created exclusions would be detected as changes to send in a following
synchronization.

closes odoo/odoo#37884

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>