https://spdx.github.io/spdx-spec/SPDX-license-expressions/ says that
using upper-case operators is canonical.
/*
* Copyright © 2010-2015 Ralf Habacker
* Copyright © 2015-2019 Collabora Ltd.
- * SPDX-License-Identifier: AFL-2.1 or GPL-2.0-or-later
+ * SPDX-License-Identifier: AFL-2.1 OR GPL-2.0-or-later
*
* Licensed under the Academic Free License version 2.1
*
/* test-platform-mutex.c
*
* Copyright © 2022 Ralf Habacker <ralf.habacker@freenet.de>
- * SPDX-License-Identifier: AFL-2.1 or GPL-2.0-or-later
+ * SPDX-License-Identifier: AFL-2.1 OR GPL-2.0-or-later
* Licensed under the Academic Free License version 2.1
*