Update xpath of shipment_in_return_form view

issue6183 changed the form layout.

view/shipment_in_return_form.xml

@@ -2,7 +2,7 @@
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
 this repository contains the full copyright notices and license terms. -->
 <data>
-    <xpath expr="/form/field[@name='moves']" position="after">
+    <xpath expr="//field[@name='moves']" position="after">
         <field name="root_packages" colspan="4"
             view_ids="stock_package.package_view_tree"/>
     </xpath>