Fix section closing tag in login page

Author: thibaudcolas

trac-env/templates/plainlogin.html

@@ -16,7 +16,7 @@ <h1>Choose how you want to log in</h1>
 <section class="login-github">
   <h2>Log in with your GitHub account</h2>
   <a href="/github/login">Log in with GitHub</a>
-<section>
+</section>
 
 <section class="login-djangoproject">
   <h2>Log in with your DjangoProject account</h2>