Add apioutput to unsupported skins

There is nothing ULS can do here: there is no entry point to change
language or access settings, there is nothing to type.

One exception would be loading web fonts. But I would argue that
that is a small set of users, who can use Special:ApiSandbox or
the wiki help pages.

Bug: T145186
Change-Id: I71de2a58f007ff03b01c9edc5ed6bed0e6524c4e

includes/UniversalLanguageSelectorHooks.php

@@ -136,7 +136,7 @@ class UniversalLanguageSelectorHooks implements
 	 * Hook: BeforePageDisplay
 	 */
 	public function onBeforePageDisplay( $out, $skin ): void {
-		$unsupportedSkins = [ 'minerva' ];
+		$unsupportedSkins = [ 'minerva', 'apioutput' ];
 		if ( in_array( $skin->getSkinName(), $unsupportedSkins ) ) {
 			return;
 		}