$ git clone -n https://src.fedoraproject.org/rpms/R-purrr.git /var/lib/mock/f45-build-6351-348/root/chroot_tmpdir/scmroot/R-purrr
Cloning into '/var/lib/mock/f45-build-6351-348/root/chroot_tmpdir/scmroot/R-purrr'...
$ git fetch origin cddf72bbd4a53cbdd26acaa8d8a358d5576d0e40:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-purrr
 * [new ref]         cddf72bbd4a53cbdd26acaa8d8a358d5576d0e40 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cddf72b Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild