improve filter for ponctual vevent exceptions (#27263)

To differentiate events between those coming from locally uploaded and remotely fetched
.ics files, we must look up the locally uploaded ones with a filter of
"recurrence_id=0".

chrono/agendas/models.py

@@ -529,6 +529,7 @@ class Desk(models.Model):
 
                 kwargs = {}
                 kwargs['desk'] = self
+                kwargs['recurrence_id'] = 0
                 if keep_synced_by_uid:
                     kwargs['external_id'] = vevent.contents['uid'][0].value
                 else: