Fix license header

Author: rjtokenring

tests/arduino/app_bricks/sound_generator/test_abc.py

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: Copyright (C) 2025 ARDUINO SA <http://www.arduino.cc>
+#
+# SPDX-License-Identifier: MPL-2.0
+
 from arduino.app_bricks.sound_generator import ABCNotationLoader