Fix TeamListView for staff members_count

Incorrect check for staff status on the user object.

src/backoffice/templates/backoffice/teams/list.html

@@ -47,7 +47,7 @@
                 <a href="{% url 'backoffice:team' uuid=team.uuid %}">{{ team.name }}</a>
               </td>
               <td>{{ team.get_visibility_display }}</td>
-              {% if user.is_staff %}<td>{{ team.members_count }}</td>{% endif %}
+              {% if conferencemember.is_staff %}<td>{{ team.members_count }}</td>{% endif %}
               <td>
                 {% if team.is_member %}
                   {{ team.is_manager|yesno }}