ui_test: ignore errors with cell/getId for testAccessUnauthorizedRelationValue

This listbox can be used to show documents that user is not allowed to
access, so this `cell/getId` can raise. In Zope2 it was raising
Unauthorized and this Unauthorized was catched, on Zope4 it is raising
NotFound, which is no longer catch since 850e436e (
Products.ERP5Form.Form: Let NotFound exceptions propagate during
rendering, 2022-11-25), so this NotFound was raised as a site error,
which caused an error in the test.

bt5/erp5_ui_test/SkinTemplateItem/portal_skins/erp5_ui_test/FooModule_viewFooList/listbox_id.xml

@@ -273,7 +273,7 @@
       <dictionary>
         <item>
             <key> <string>_text</string> </key>
-            <value> <string>cell/getId</string> </value>
+            <value> <string>cell/getId | nothing</string> </value>
         </item>
       </dictionary>
     </pickle>