403 forbidden dismissing event notification

[gnagn0]

Describe the problem and steps to reproduce it:

Could not dismiss notifications or change/update calendar items.
Version: 91.0.4
Thunderbird version: 91.7.0

Log from error console:

Calendar: [calGoogleCalendar] Modifying item XXXXXX failed:2147500037: {
 "error": {
  "errors": [
   {
    "domain": "calendar",
    "reason": "forbiddenForNonOrganizer",
    "message": "Shared properties can only be changed by the organizer of the event."
   }
  ],
  "code": 403,
  "message": "Shared properties can only be changed by the organizer of the event."
 }
}

[kewisch]

See #3