fixes #4251

Closes #4251

Merge request studip/studip!3081

templates/shared/tooltip.php

+<?php
+/**
+ * @var bool $important
+ * @var bool $html
+ * @var string $text
+ */
+?>
 <span class="tooltip tooltip-icon <? if ($important) echo 'tooltip-important'; ?>"
-      tabindex="0" aria-label="<?= $html ? kill_format($text) : htmlReady($text) ?>">
+      tabindex="0" aria-label="<?= $html ? htmlReady(strip_tags($text)) : htmlReady($text) ?>">
     <span class="tooltip-content"><?= $html ? $text : htmlReady($text) ?></span>
 </span>