Do not call _changed_values as it is a property

92a025702d76 backported a usage that is not in 7.0 series as the
_changed_values is still a property instead of a method.

--HG--
branch : 7.0

modules/web_shop_shopify/sale.py

@@ -372,7 +372,7 @@ class Line(IdentifierMixin, metaclass=PoolMeta):
                 setattr_changed(line, 'product', product)
         if line.product:
             line._set_shopify_quantity(line.product, quantity)
-            if line._changed_values():
+            if line._changed_values:
                 line.on_change_product()
         else:
             setattr_changed(line, 'quantity', quantity)