Fix a missing closing div due to r21312 (#35755, #36326).

Contributed by Enziin System.


git-svn-id: http://svn.redmine.org/redmine/trunk@21318 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/views/settings/_authentication.html.erb

@@ -39,6 +39,7 @@
   </em>
 </p>
 
+</div>
 
 <fieldset class="box">
   <legend><%= l(:label_session_expiration) %></legend>