[FIX] hr_equipment: no technician subscribe in 9.0

In 9.0, an "Human Resources / Employee" see only hr.equipment for which
they are set as the "Employee".

But the code automatically subscribed the "Technician" because the field
name was named technically "user_id" which is automatically subscribed
by the system.

This led to a possible issue with read / unread message because of
feature that just happen by coincidence.

For 9.0 only (in 10.0 the field has been renamed technician_user_id and
access rules have been changed).

opw-805185
closes odoo#22273

addons/hr_equipment/models/hr_equipment.py

@@ -182,6 +182,15 @@ def write(self, vals):
             self.message_subscribe_users(user_ids=user_ids)
         return super(HrEquipment, self).write(vals)
 
+    @api.model
+    def _message_get_auto_subscribe_fields(self, updated_fields, auto_follow_fields=None):
+        """ mail.thread override so user_id which has no special access allowance is not
+            automatically subscribed.
+        """
+        if auto_follow_fields is None:
+            auto_follow_fields = []
+        return super(HrEquipment, self)._message_get_auto_subscribe_fields(updated_fields, auto_follow_fields)
+
     @api.multi
     def _read_group_category_ids(self, domain, read_group_order=None, access_rights_uid=None):
         """ Read group customization in order to display all the category in the