[FIX] purchase_discount: Use sudo in purchase lines

purchase_discount/models/stock_move.py

@@ -13,7 +13,10 @@ def _get_price_unit(self):
         maximum inheritability.
         """
         price_unit = False
-        po_line = self.purchase_line_id
+        # We do it with sudo to avoid permission errors in case
+        # the user validates the order and does not have permission to
+        # modifiy purchase lines
+        po_line = self.purchase_line_id.sudo()
         if po_line and self.product_id == po_line.product_id:
             price = po_line._get_discounted_price_unit()
             if price != po_line.price_unit: