$ git clone -n https://src.fedoraproject.org/rpms/R-desc.git /var/lib/mock/f45-build-6050-346/root/chroot_tmpdir/scmroot/R-desc
Cloning into '/var/lib/mock/f45-build-6050-346/root/chroot_tmpdir/scmroot/R-desc'...
$ git fetch origin 03994037a6683b85c8917c400d94a8b51e25c926:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-desc
 * [new ref]         03994037a6683b85c8917c400d94a8b51e25c926 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0399403 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild