[FIX] l10n_be_hr_payroll: Store existing field company_car_total_depreciated_cost

Purpose
=======

In l10n_be_hr_payroll, the field is a simple Float field, it implied `store=True`
In l10n_be_hr_payroll_fleet, a compute method is added, and becomes `store=False`

Specification
=============

Keep this field `store=True`. This could only be done because the column already exists in the database.

PS: Same reason for car_atn

addons/l10n_be_hr_payroll_fleet/models/hr_contract.py

@@ -11,8 +11,8 @@ class HrContract(models.Model):
         domain=lambda self: self._get_available_cars_domain(),
         default=lambda self: self.env['fleet.vehicle'].search([('driver_id', '=', self.employee_id.address_home_id.id)], limit=1),
         help="Employee's company car.")
-    car_atn = fields.Float(compute='_compute_car_atn_and_costs', string='ATN Company Car')
-    company_car_total_depreciated_cost = fields.Float(compute='_compute_car_atn_and_costs')
+    car_atn = fields.Float(compute='_compute_car_atn_and_costs', string='ATN Company Car', store=True)
+    company_car_total_depreciated_cost = fields.Float(compute='_compute_car_atn_and_costs', store=True)
     available_cars_amount = fields.Integer(compute='_compute_available_cars_amount', string='Number of available cars')
     new_car = fields.Boolean('Request a new car')
     new_car_model_id = fields.Many2one('fleet.vehicle.model', string="Model", domain=lambda self: self._get_possible_model_domain())