base: fix login listbox title

according to https://www.erp5.com/bt5-Module.Creation.Guidelines *3.3 Listbox rules*

> If a listbox is configured so that only objects from one portal type can be displayed, then the title of the listbox should be set to the plural of the given portal type title (ex : Sale Orders should be the title of a listbox displaying "Sale Order" objects).

bt5/erp5_base/SkinTemplateItem/portal_skins/erp5_base/Person_viewAssignment/login_listbox.xml

@@ -149,7 +149,7 @@
                 </item>
                 <item>
                     <key> <string>title</string> </key>
-                    <value> <string>Login</string> </value>
+                    <value> <string>Logins</string> </value>
                 </item>
                 <item>
                     <key> <string>width</string> </key>