[FIX] hr_holidays: Don't reset leave manager only if manually changed

When changing an employee's parent_id, the leave_manager_id
should be updated to the new parent_id's user, UNLESS
leave_manager_id was changed manually.
i.e leave_manager_id != previous parent_id

closes odoo/odoo#37190

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

addons/hr_holidays/models/hr_employee.py

@@ -154,7 +154,10 @@ class HrEmployeeBase(models.AbstractModel):
     def write(self, values):
         if 'parent_id' in values:
             manager = self.env['hr.employee'].browse(values['parent_id']).user_id
-            values['leave_manager_id'] = values.get('leave_manager_id', manager.id)
+            if manager:
+                to_change = self.filtered(lambda e: e.leave_manager_id == e.parent_id.user_id or not e.leave_manager_id)
+                to_change.write({'leave_manager_id': values.get('leave_manager_id', manager.id)})
+
         res = super(HrEmployeeBase, self).write(values)
         if 'parent_id' in values or 'department_id' in values:
             today_date = fields.Datetime.now()