base: add Notification Message in document portal type group

So that version view works as expected, see b415abbb (dms: add version
view on notification messages, 2024-06-19)

bt5/erp5_base/PortalTypeTemplateItem/portal_types/Notification%20Message.xml

@@ -33,7 +33,9 @@
         <item>
             <key> <string>group_list</string> </key>
             <value>
-              <tuple/>
+              <tuple>
+                <string>document</string>
+              </tuple>
             </value>
         </item>
         <item>