Added header license to test_to_skip.php

Author: ezimuel

tests/test_to_skip.php

@@ -1,4 +1,16 @@
 <?php
+/**
+ * Elasticsearch PHP Client
+ *
+ * @link      https://github.com/elastic/elasticsearch-php
+ * @copyright Copyright (c) Elasticsearch B.V (https://www.elastic.co)
+ * @license   https://opensource.org/licenses/MIT MIT License
+ *
+ * Licensed to Elasticsearch B.V under one or more agreements.
+ * Elasticsearch B.V licenses this file to you under the MIT License.
+ * See the LICENSE file in the project root for more information.
+ */
+
 // A list of tests in elasticsearch-clients-tests to be skipped
 return [
     'cat/aliases.yml',