[FLINK-13728][docs] Fix wrong closing tag order in sidenav

This closes apache#9439

docs/_includes/sidenav.html

@@ -88,7 +88,7 @@
  {% else %}
  {% assign elementsPos = elementsPosStack | last %}
  {% assign pos = posStack | last %}
-</li></ul></div>
+</ul></div></li>
  {% assign elementsPosStack = elementsPosStack | pop %}
  {% assign posStack = posStack | pop %}
  {% endif %}