[FIX]sale_stock: copy devolution move without decreasing respective SO values

-Make a return picking from a SO, and condigure the items to be refunded on SO(in the wizard)
-Copy the return picking.
-Validate it.

Without this fix, it would just keep decreasing the delivered value on SO.

opw:767429

addons/sale_stock/models/stock.py

@@ -14,7 +14,7 @@ class StockMove(models.Model):
     _inherit = "stock.move"
 
     to_refund_so = fields.Boolean(
-        "To Refund in SO", default=False,
+        "To Refund in SO", copy=False, default=False,
         help='Trigger a decrease of the delivered quantity in the associated Sale Order')
 
     @api.multi