docs/website/sponsors.html: fix page layout

The LTS block was glued with the next block, add missing </div>.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

docs/website/sponsors.html

@@ -13,6 +13,7 @@
          Program</a>.</p>
       <p>When the Buildroot LTS Sponsoring program will be operational
          later in 2024, those sponsors will be mentioned here.</p>
+      </div>
     </div>
 
     <div class="panel panel-primary">