[test] added missing copyright block

server/test/board/crossover.cpp

@@ -1,3 +1,24 @@
+/**
+ * This file is part of Traintastic,
+ * see <https://github.com/traintastic/traintastic>.
+ *
+ * Copyright (C) 2025 Reinder Feenstra
+ *
+ * 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 2
+ * 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, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
 #include <catch2/catch_template_test_macros.hpp>
 #include "../src/world/world.hpp"
 #include "../src/core/method.tpp"