[FIX] website: don't show empty burger menu on mobile

When the current app doesn't provide menu-items (or the user doesn't
have the rights to access them), the mobile burger menu should fallback
to the user menu instead of an empty one (like on the App Switcher).

task-2345001

closes odoo/odoo#77161

Signed-off-by: Romain Derie (rde) <rde@odoo.com>

addons/website/views/website_navbar_templates.xml

@@ -33,7 +33,7 @@
                     </li>
                 </ul>
 
-                <button type="button" class="fa fa-bars float-right d-block d-md-none o_mobile_menu_toggle" aria-label="Menu" title="Menu"/>
+                <button type="button" class="fa fa-bars float-right d-block d-md-none o_mobile_menu_toggle" aria-label="Menu" title="Menu" groups="website.group_website_designer"/>
 
                 <ul class="o_menu_sections" groups="website.group_website_designer">
                     <!-- Content -->