I'm setting the license for the project as GPL-3.0-only
Please ignore any indication in the repo or GitLab UI that says
otherwise.

Rationale:

While `R` itself is dual licensed under the GPL-v2.0 and the GPL-v3.0,
some dependencies (present or future) are licensed only under the
GPL-3.0.

GPL-3.0 code can include code licensed under the GPL-v2.0-or-later, as
clarified by the FSF.

However, from my understanding, code licensed under the GPL-2.0-or-later
cannot include GPL-3.0, as that would mean the derived work could be
released under the GPL-2.0, effectively causing the license to regress.

Hence, I'm bumping the license to GPL-v3.0-only.

I'm not sure whether GitLab will display it as GPL-v3.0-only or as
GPL-v3.0-or-later.

I'm afraid, this project might have to be licensed GPL-3.0-only,
given some dependencies might not state if they're compatible with
possible later versions of the GPL. It is my understanding that if they
do not specify that they are to be treated as GPL-v3.0-only and
incompatible with GPL-v3.0-or-later.