Trac 57662 test plugin -- enables custom WordPress package update

fake-wordpress-update.php

<?php
/**
 * Plugin Name: Fake WordPress Update
 * Description: Filters the value of <code>site_transient_update_core</code> to allow a custom install package.
 * Author:      WordPress Core Contributors
 * Author URI:  https://make.wordpress.org/core
 * License:     GPLv2 or later
 * Version:     1.0.0
 *
 * Adapted from https://gist.githubusercontent.com/hellofromtonya/bb0aa2d4b2311c8b40fa5ae8ada4dc19
 */

add_filter(
    'site_transient_update_core',
    function ( $value ) {
        if ( ! isset( $value->updates ) ) {
            return $value;
        }
        
        $fake_update_location = trailingslashit( get_bloginfo( 'url' ) ) . 'wordpress-custom.zip';
        $fake_update          = (object) array(
            'response' => 'upgrade',
            'download' => $fake_update_location,
            'locale' => 'en_US',
            'packages' => 
            (object) array(
                'full' => $fake_update_location,
                'no_content' => $fake_update_location,
                'new_bundled' => $fake_update_location,
                'partial' => '',
                'rollback' => '',
            ),
            'current' => '6.3.0-custom',
            'version' => '6.3.0-custom',
            'php_version' => '5.6.20',
            'mysql_version' => '5.0',
            'new_bundled' => '6.3',
            'partial_version' => '',
            'version_checked' => '',
        );

        array_unshift( $value->updates, $fake_update );

        return $value;
    }
);

On 2023-06-27 updated plugin to fake version 6.3.0-custom for Trac 58206 testing.