fix: COMPOSER_PATH may be false

PHP Fatal error:  Uncaught TypeError: is_file(): Argument #1 ($filename) must be of type string, bool given in /home/runner/work/CodeIgniter4/CodeIgniter4/system/Autoloader/Autoloader.php:126

Author: kenjis

system/Test/bootstrap.php

@@ -46,7 +46,7 @@
 defined('FCPATH')        || define('FCPATH', realpath(PUBLICPATH) . DIRECTORY_SEPARATOR);
 defined('TESTPATH')      || define('TESTPATH', realpath(HOMEPATH . 'tests/') . DIRECTORY_SEPARATOR);
 defined('SUPPORTPATH')   || define('SUPPORTPATH', realpath(TESTPATH . '_support/') . DIRECTORY_SEPARATOR);
-defined('COMPOSER_PATH') || define('COMPOSER_PATH', realpath(HOMEPATH . 'vendor/autoload.php'));
+defined('COMPOSER_PATH') || define('COMPOSER_PATH', (string) realpath(HOMEPATH . 'vendor/autoload.php'));
 defined('VENDORPATH')    || define('VENDORPATH', realpath(HOMEPATH . 'vendor') . DIRECTORY_SEPARATOR);
 
 // Load Common.php from App then System