Display non field errors on create and edit

wagtail/admin/templates/wagtailadmin/generic/form.html

@@ -6,6 +6,8 @@
     <form action="{{ action_url }}" method="POST" novalidate{% if form.is_multipart %} enctype="multipart/form-data"{% endif %}>
         {% csrf_token %}
 
+        {{ form.non_field_errors }}
+
         {% block hidden_fields %}
             {% for field in form.hidden_fields %}{{ field }}{% endfor %}
         {% endblock %}