Explicitly use configuration file from fixture directory

Author: sebastianbergmann

tests/end-to-end/regression/5487.phpt

@@ -3,6 +3,7 @@ https://github.com/sebastianbergmann/phpunit/issues/5487
 --FILE--
 <?php declare(strict_types=1);
 $_SERVER['argv'][] = '--do-not-cache-result';
+$_SERVER['argv'][] = '--configuration';
 $_SERVER['argv'][] = __DIR__ . '/5487';
 
 require_once __DIR__ . '/../../bootstrap.php';