remove toggle button for secondary sidebar if empty (#1637)

Author: PierreMarchand20

src/pydata_sphinx_theme/theme/pydata_sphinx_theme/sections/header.html

@@ -39,7 +39,7 @@
     </div>
   {% endfor %}
 
-  {% if not remove_sidebar_secondary %}
+  {% if not remove_sidebar_secondary and secondary_sidebar_items %}
     <label class="sidebar-toggle secondary-toggle" for="__secondary" tabindex="0">
       <span class="fa-solid fa-outdent"></span>
     </label>