[FIX] hr_holidays: Include manager (parent_id) as valid responsible

On a time off request, if the 'Time Off Responsible' (leave_manager_id)
is not set, then the SUPERUSER_ID is taken as time off responsible for the
validation.

Before falling back on OdooBot, include the parent_id of the employee,
aka the manager, as a valid responsible.

closes odoo/odoo#37506

Task: 2072111
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/hr_holidays/models/hr_leave.py

@@ -917,6 +917,8 @@ class HolidaysRequest(models.Model):
         if self.validation_type == 'manager' or (self.validation_type == 'both' and self.state == 'confirm'):
             if self.employee_id.leave_manager_id:
                 responsible = self.employee_id.leave_manager_id
+            elif self.employee_id.parent_id.user_id:
+                responsible = self.employee_id.parent_id.user_id
         elif self.validation_type == 'hr' or (self.validation_type == 'both' and self.state == 'validate1'):
             if self.holiday_status_id.responsible_id:
                 responsible = self.holiday_status_id.responsible_id