HostnameValidator: Update copyright and license

src/HostnameValidator.vala

@@ -1,20 +1,7 @@
-// -*- Mode: vala; indent-tabs-mode: nil; tab-width: 4 -*-
-/*-
+/*
+ * Copyright 2018-2022 System76 <[email protected]>
  * Copyright 2024 elementary, Inc. (https://elementary.io)
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- *
- * Authored by: Marius Meisenzahl <[email protected]>
+ * SPDX-License-Identifier: MIT
  */
 
 namespace Utils {