[FIX] mrp : Auto-fill Number of SN for mass produce

Current Behaviour :
When mass producing with SN, the default number of SN to generate is set to 0.
Behaviour after the PR :
When mass producing with SN, the default number of SN to generate is the number of item to produce.

opw-2680306

closes odoo/odoo#79431

X-original-commit: 38e5d002acc2e516987acc0afe38648473fff708
Signed-off-by: Arnold Moyaux <arm@odoo.com>
Signed-off-by: Damhaut Florian (flda) <flda@odoo.com>

addons/mrp/models/mrp_production.py

@@ -1752,6 +1752,7 @@ class MrpProduction(models.Model):
             'default_production_id': self.id,
             'default_expected_qty': self.product_qty,
             'default_next_serial_number': next_serial,
+            'default_next_serial_count': self.product_qty - self.qty_produced,
         }
         return action