summary: include list of formdatas if there are multiple ones (#8517)

welco/sources/mail/templates/welco/mail_summary.html

@@ -4,3 +4,12 @@
  <img src="{{ site_base }}{{ object.content.url }}.png" alt=""/>
  </a>
 </p>
+
+{% if object.associations.all|length > 1 %}
+<strong>{% trans 'Mail with multiple formdata:' %}</strong>
+<ul>
+{% for association in object.associations.all %}
+  <li><a href="{{association.formdata_url}}">{{association.formdef_name}}</a></li>
+{% endfor %}
+</ul>
+{% endif %}