[FIX] fleet: store driver on log services

Changing the driver on a car shouldn't change the
fleet.vehicle.log.services associated. We should keep the driver
assigned to the car at the time the service was done.

closes odoo/odoo#54264

Taskid: 2208080
X-original-commit: 5422bb8d6e3db5d6932570116af74ea634c40a51
Signed-off-by: Paul Morelle <madprog@users.noreply.github.com>

addons/fleet/models/fleet_vehicle_cost.py

@@ -151,7 +151,7 @@ class FleetVehicleLogServices(models.Model):
     date = fields.Date(help='Date when the cost has been executed')
     company_id = fields.Many2one('res.company', 'Company', default=lambda self: self.env.company)
     currency_id = fields.Many2one('res.currency', related='company_id.currency_id')
-    purchaser_id = fields.Many2one(related='vehicle_id.driver_id', string="Driver")
+    purchaser_id = fields.Many2one('res.partner', string="Driver", compute='_compute_purchaser_id', readonly=False, store=True)
     inv_ref = fields.Char('Vendor Reference')
     vendor_id = fields.Many2one('res.partner', 'Vendor')
     notes = fields.Text()
@@ -188,4 +188,9 @@ class FleetVehicleLogServices(models.Model):
                 # data as it would result to the creation of a
                 # odometer log with 0, which is to be avoided
                 del data['odometer']
-        return super(FleetVehicleLogServices, self).create(vals_list)
+        return super(FleetVehicleLogServices, self).create(vals_list)
+
+    @api.depends('vehicle_id')
+    def _compute_purchaser_id(self):
+        for service in self:
+            service.purchaser_id = service.vehicle_id.driver_id