fix permission_callback value updated by mistake

lib/experimental/fonts/font-library/class-wp-rest-font-families-controller.php

@@ -44,8 +44,7 @@ public function register_routes() {
 				array(
 					'methods'             => WP_REST_Server::READABLE,
 					'callback'            => array( $this, 'get_items' ),
-					'permission_callback' => function () {
-						return true;},
+					'permission_callback' => array( $this, 'update_font_library_permissions_check' ),
 				),
 			)
 		);