chore(tests): Cleanup bootstrap.php to be forward-compatible

Signed-off-by: Robin Appelman <robin@icewind.nl>

Author: icewind1991

tests/bootstrap.php

@@ -6,13 +6,19 @@
  * SPDX-FileCopyrightText: 2017 Nextcloud GmbH and Nextcloud contributors
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
-define('PHPUNIT_RUN', 1);
+
+use OCP\App\IAppManager;
+use OCP\Server;
+
+if (!defined('PHPUNIT_RUN')) {
+	define('PHPUNIT_RUN', 1);
+}
 
 require_once __DIR__ . '/../../../lib/base.php';
 require_once __DIR__ . '/../vendor/autoload.php';
 
 require_once __DIR__ . '/../../../tests/autoload.php';
 
-\OC_App::loadApp('circles');
+Server::get(IAppManager::class)->loadApp('circles');
 
 OC_Hook::clear();