Add 'block.super' to snippets/type_index.html

wagtail/wagtailsnippets/templates/wagtailsnippets/snippets/type_index.html

@@ -4,6 +4,7 @@
 
 {% block extra_js %}
     <script>
+        {{ block.super }}
         window.headerSearch = {
             url: "{% url 'wagtailsnippets:list' content_type.app_label content_type.model %}",
             termInput: "#id_q",