(devel/R-checkmate) Updated 2.2.0 to 2.3.1

# Version 2.3.1
* Fixed a sprintf format string for long integers.

# Version 2.3.0
* `NULL` is not longer considered to be atomic in future versions of R
  (c.f. <https://stat.ethz.ch/pipermail/r-devel/2023-September/082892.html>).
  To avoid breaking reverse dependencies, checkmate will stick to the old
  behavior until further notice.
* Fixed a warning in `checkAtomic()` (#245).

(mef)