Docs - fix small typo in HTML layout

docs/_templates/layout.html

@@ -37,7 +37,7 @@
         /**
          * Return true (debug: on) for local builds or Read the Docs PR previews.
          *
-         * The debug mode allows inspection of the dropodown.
+         * The debug mode allows inspection of the dropdown.
          */
         function getSearchDebugMode() {
             let debug = false