[FIX] stock_landed_costs: do not prorate

- Set the product A in FIFO, real-time valuation
- Receive 5 units @ 2000 each
- Create a landed cost of 1000, apply on the picking
  => the cost of A is 2200
- Sell one unit
- Create another landed cost of 1000, apply on the same picking

The cost of A is 2360, while one expects 2400.

The value of the move after the second landed cost is computed as:
value = previous value + prorata of landed cost 2
      = 11000 + (1000 * 4/5)
      = 11800

This is not correct. The whole value of the second landed cost should be
taken into account for the `value` field. The prorata is only useful for
the field `remaining_value`.

opw-1878229

addons/stock_landed_costs/models/stock_landed_cost.py

@@ -107,9 +107,9 @@ class LandedCost(models.Model):
                 new_landed_cost_value = line.move_id.landed_cost_value + line.additional_landed_cost
                 line.move_id.write({
                     'landed_cost_value': new_landed_cost_value,
-                    'value': line.move_id.value + cost_to_add,
+                    'value': line.move_id.value + line.additional_landed_cost,
                     'remaining_value': line.move_id.remaining_value + cost_to_add,
-                    'price_unit': (line.move_id.value + cost_to_add) / line.move_id.product_qty,
+                    'price_unit': (line.move_id.value + line.additional_landed_cost) / line.move_id.product_qty,
                 })
                 # `remaining_qty` is negative if the move is out and delivered proudcts that were not
                 # in stock.