Fix 404 in search pages.

Fix #6210

docs/_templates/layout.html

@@ -90,7 +90,7 @@
         <option value="{{ pathto(p + '/index')|e }}" {% if pagename is prefixedwith p %}selected{% endif %}>{{ ext }}</option>
         {%- endfor %}
       </select>
-      <form role="search" class="search" action="search.html" method="get">
+      <form role="search" class="search" action="{{ pathto('search') }}" method="get">
         <div class="search-wrapper">
           <input type="search" name="q" placeholder="{{ _('Search documentation') }}" />
           <button type="submit">