[MAINTENANCE] Add class for ul element in TOC Plugin (kitodo#1845)

Co-authored-by: Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>

Author: beatrycze-volk

Resources/Private/Templates/TableOfContents/Main.html

@@ -13,7 +13,7 @@
       data-namespace-typo3-fluid="true">
 
 <div class="tx-dlf-tableofcontents">
-    <ul>
+    <ul class="tx-dlf-tableofcontents-list">
         <f:render partial="TableOfContents/Children" arguments="{children: toc, viewData: viewData}"/>
     </ul>
 </div>