Tests: add missing file header

Author: glaubinix

tests/Api/TokensTest.php

@@ -1,4 +1,11 @@
-<?php declare(strict_types=1);
+<?php
+
+/*
+ * (c) Packagist Conductors GmbH <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
 
 namespace PrivatePackagist\ApiClient\Api;