[FIX] hr_fleet: fixes demo data vehicle assignation logs

In the demo data from hr_fleet, we add address_home_id's to some employees in
order to create the correct vehicle assignation logs. However, as the driver_id
is already set at that moment, the _compute_driver_employee_id is not called
again as no dependency was changed, resulting in an empty driver_employee_id
for some logs. This commit fixes this by calling the compute method on the demo
data with the assignation logs that have no driver_employee_id set and have a
driver_id.

task-2742923

Part-of: odoo/odoo#83755

addons/hr_fleet/data/hr_fleet_demo.xml

@@ -29,4 +29,10 @@
     <record id="fleet.vehicle_5" model="fleet.vehicle">
         <field name="driver_employee_id" ref="hr.employee_jep"/>
     </record>
+
+    <!-- recompute driver_employee_id as we assigned a proper address_home_id to some employees -->
+    <function model="fleet.vehicle.assignation.log" name="_compute_driver_employee_id">
+        <value model="fleet.vehicle.assignation.log" eval="obj().search([('driver_employee_id', '=', False), ('driver_id', '!=', False)]).ids"/>
+    </function>
+
 </odoo>