[FIX] google_calendar: Prevent resyncing of synced recurrence events

Before this commit: When you sync the Odoo calendar with Google for the
first time, it will resync all of the created recurrence events with
Google after fetching all of the Google events. The problem is that it
chooses the 'accepted' state by default for the current user's state.
If you were invited to events and you hadn't accepted that, it would
update your status and send an email per event for all attendees.

Steps to reproduce the issue:
 1. Create two new google accounts ( you'll bombard with emails)
 2. Create a recurrent event without ending with the first account and
choose the second account as a guest.(don't accept)
 3. Sync second account with Odoo
  => It'll send about 700 emails

The solution is to prevent synced recurrence events from syncing and.

opw-2691146

closes odoo/odoo#89633

X-original-commit: 084aeb239e85a4e3abb3e233af68c6838dfbb3d7
Signed-off-by: Arnaud Joset <arj@odoo.com>

addons/google_calendar/models/res_users.py

@@ -73,6 +73,7 @@ class User(models.Model):
         recurrences -= synced_recurrences
         recurrences._sync_odoo2google(calendar_service)
         synced_events |= recurrences.calendar_event_ids - recurrences._get_outliers()
+        synced_events |= synced_recurrences.calendar_event_ids - synced_recurrences._get_outliers()
         events = self.env['calendar.event']._get_records_to_sync(full_sync=full_sync)
         (events - synced_events)._sync_odoo2google(calendar_service)