[FIX] stock: don't replace product/inventory view groups

The current view replaces the existing groups attribute of the inventory
page in the product template form view with two specified groups (with
only one of these groups being newly introduced in stock).

This commit changes the product view to utilise an xpath that adds the
single new group (stock.group_stock_user), instead of replacing the
content of the attributes.

closes odoo/odoo#119223

X-original-commit: 43c888bb
Related: odoo/enterprise#40085
Signed-off-by: Brice Bartoletti (bib) <bib@odoo.com>
Signed-off-by: Daniel Kosky (dako) <dako@odoo.com>

addons/stock/views/product_views.xml

@@ -145,9 +145,9 @@
                         </group>
                     </group>
                 </page>
-                <page name="inventory" position="attributes">
-                    <attribute name="groups">stock.group_stock_user,product.group_stock_packaging</attribute>
-                </page>
+                <xpath expr="//page[@name='inventory']" position="attributes">
+                    <attribute name="groups" add="stock.group_stock_user" separator=","/>
+                </xpath>
             </field>
         </record>