Restore setup pincode following [57adc5d]

'57adc5d120 - Flatten the Setup Menus in the default menu theme' dropped util_menu.xml but failed to carry over the <password> markup.

Fixes #10950

mythtv/themes/defaultmenu/mainmenu.xml

@@ -41,6 +41,7 @@
         <text>Setup</text>
         <description>Configure MythTV and plugins</description>
         <action>MENU main_settings.xml</action>
+        <password>SetupPinCode</password>
     </button>
 
 </mythmenu>