$ git clone -n https://src.fedoraproject.org/rpms/R-pkgcache.git /var/lib/mock/f45-build-6308-347/root/chroot_tmpdir/scmroot/R-pkgcache
Cloning into '/var/lib/mock/f45-build-6308-347/root/chroot_tmpdir/scmroot/R-pkgcache'...
$ git fetch origin f21c3a0c3ee033884d49aeae72a8724f42c3ee3c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-pkgcache
 * [new ref]         f21c3a0c3ee033884d49aeae72a8724f42c3ee3c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f21c3a0 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild