wordcamp-bristol-2019/wp-admin/ms-upgrade-network.php

<?php
/**
 * Multisite upgrade administration panel.
 *
 * @package WordPress
 * @subpackage Multisite
 * @since 3.0.0
 */

require_once( dirname( __FILE__ ) . '/admin.php' );

wp_redirect( network_admin_url( 'upgrade.php' ) );
exit;