License Question: Which one was used by this project, GPL-3.0-only or GPL-3.0-or-later

I maintain the package of this project in [archlinuxcn](https://github.com/archlinuxcn/repo). Recently, Arch Linux enforced using the SPDX identifier via RFC16[^1]. It differs from GPL-3.0-only and GPL-3.0-or-later. So I need to know which one was used in this project.
Thank You!

[^1]: https://gitlab.archlinux.org/archlinux/rfcs/-/blob/master/rfcs/0016-spdx-license-identifiers.rst