[FIX] mrp: do not split additional product

On a production, additional are supposed to be linked to the current
lot/serial number and not to the total production like the raw component
on the BoM.
This commit do not split stock move for those product anymore at the
backorder creation.

Task : 2278147

addons/mrp/models/mrp_production.py

@@ -1395,13 +1395,15 @@ class MrpProduction(models.Model):
                 })
             else:
                 for move in production.move_raw_ids | production.move_finished_ids:
-                    new_move = self.env['stock.move'].browse(move._split(move.product_uom_qty - move.unit_factor * production.qty_producing))
-                    if move.raw_material_production_id:
-                        new_move.raw_material_production_id = backorder_mo.id
-                    else:
-                        new_move.production_id = backorder_mo.id
-                    (move | new_move)._do_unreserve()
-                    (move | new_move)._action_assign()
+                    if not move.additional:
+                        qty_to_split = move.product_uom_qty - move.unit_factor * production.qty_producing
+                        new_move = self.env['stock.move'].browse(move._split(qty_to_split))
+                        if move.raw_material_production_id:
+                            new_move.raw_material_production_id = backorder_mo.id
+                        else:
+                            new_move.production_id = backorder_mo.id
+                        (move | new_move)._do_unreserve()
+                        (move | new_move)._action_assign()
             backorders |= backorder_mo
             for wo in backorder_mo.workorder_ids:
                 wo.qty_produced = 0