[FIX] hr_fleet: count distinct vehicle_id per driver

closes odoo/odoo#39249

Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>
Co-authored-by: Lucas Lefèvre <lul@odoo.com>

addons/hr_fleet/models/employee.py

@@ -26,8 +26,11 @@ class Employee(models.Model):
     def _compute_employee_cars_count(self):
         driver_ids = (self.mapped('user_id.partner_id') | self.sudo().mapped('address_home_id')).ids
         fleet_data = self.env['fleet.vehicle.assignation.log'].read_group(
-            domain=[('driver_id', 'in', driver_ids)], fields=['driver_id'], groupby=['driver_id'])
-        mapped_data = {m['driver_id'][0]: m['driver_id_count'] for m in fleet_data}
+            domain=[('driver_id', 'in', driver_ids)], fields=['vehicle_id:array_agg'], groupby=['driver_id'])
+        mapped_data = {
+            group['driver_id'][0]: len(set(group['vehicle_id']))
+            for group in fleet_data
+        }
         for employee in self:
             drivers = employee.user_id.partner_id | employee.sudo().address_home_id
             employee.employee_cars_count = sum(mapped_data.get(pid, 0) for pid in drivers.ids)