test/nbt_writestring_failure_mode: Add license information

src/test/nbt_writestring_failure_mode.cpp

@@ -1,3 +1,18 @@
+// Copyright 2022, FOSS-VG Developers and Contributers
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, version 3.
+//
+// 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// version 3 along with this program.
+// If not, see https://www.gnu.org/licenses/agpl-3.0.en.html
+
 #include <string>
 #include <vector>
 #include <iostream>