refs #19231 [finc] Section landmark for modal

* wraps modal in a <section> for accessibility

co-authored by: Alexander Purr <purr@ub.uni-leipzig.de>

themes/finc/templates/layout/layout.phtml

@@ -285,7 +285,8 @@ if (!isset($this->layout()->searchbox)) {
 <?=$this->render('footer.phtml')?>
 
 <!-- MODAL IN CASE WE NEED ONE -->
-<?php /* finc: move X button to logical pos. in structure + use 'aria-describedby' instead of 'aria-labelledby - CK */ ?>
+  <section>
+  <?php /* finc: move X button to logical pos. in structure + use 'aria-describedby' instead of 'aria-labelledby - CK */ ?>
     <div id="modal" class="modal fade hidden-print" tabindex="-1" role="dialog" aria-modal="true" aria-hidden="true" aria-describedby="modal-description">
       <div class="modal-dialog">
         <div class="modal-content">
@@ -298,6 +299,8 @@ if (!isset($this->layout()->searchbox)) {
         </div>
       </div>
     </div>
+  </section>
+
     <div class="offcanvas-overlay" data-toggle="offcanvas"></div>
     <?=$this->googleanalytics()?>
     <?=$this->piwik()?>