Using h4 for sub headings in debug table

Author: mamazu

templates/Collector/db.html.twig

@@ -420,7 +420,7 @@
                 {% else %}
                     {% for manager, classes in collector.entities %}
                         {% if collector.managers|length > 1 %}
-                            <h3>{{ manager }} <small>entity manager</small></h3>
+                            <h4>{{ manager }} <small>entity manager</small></h4>
                         {% endif %}
 
                         {% if classes is empty %}