Fix table broke by other change

schools/templates/schools/activities.html

@@ -20,6 +20,7 @@
         <tr>
           <th>{% trans "Start" %}</th>
           <th>{% trans "End" %}</th>
+          <th>{% trans "School" %}</th>
           <th>{% trans "User" %}</th>
           <th>{% trans "Description" %}</th>
           <th></th>