[FIX] hr_holidays: Link the calendar.event to hr.leave record

Steps to reproduce:

  - Install `Time Off` module
  - Create a new time off and validate it
  - Go to Calendar and check that the time off is present
  - Go back to the time off and refuse it
  - Go back to the Calendar

Issue:

  Event still present in the calendar.

Cause:

  Time off not linked to the calendar event.

Solution:

  Link the calendar.event record to the hr.leave record.

cherry-pick: https://github.com/odoo/odoo/commit/ff865dc5c97149d69cfc544877f36374a14916c5



opw-3109352

closes odoo/odoo#108925

Signed-off-by: Kevin Baptiste <kba@odoo.com>

addons/hr_holidays/models/hr_leave.py

@@ -919,6 +919,7 @@ class HolidaysRequest(models.Model):
                 'privacy': 'confidential',
                 'event_tz': user.tz,
                 'activity_ids': [(5, 0, 0)],
+                'res_id': holiday.id,
             }
             # Add the partner_id (if exist) as an attendee
             if user and user.partner_id: