changed icon html from <i> to <span>

TNL-4651

lms/static/js/fixtures/edxnotes/toggle_notes.html

@@ -1,7 +1,7 @@
 <div class="wrapper-utility edx-notes-visibility">
   <span class="action-toggle-message">Notes visible</span>
   <button class="utility-control utility-control-button action-toggle-notes is-disabled is-active" aria-pressed="true">
-    <i class="icon fa fa-pencil"></i>
+    <span class="icon fa fa-pencil" aria-hidden="true"></span>
      <span class="utility-control-label sr">Hide notes</span>
   </button>
 </div>