$ git clone -n https://src.fedoraproject.org/rpms/R-chron.git /var/lib/mock/f38-build-724205-99404/root/chroot_tmpdir/scmroot/R-chron
Cloning into '/var/lib/mock/f38-build-724205-99404/root/chroot_tmpdir/scmroot/R-chron'...
$ git fetch origin aac66a82affd1c02a6cf115c8d8f296675bec648:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-chron
 * [new ref]         aac66a82affd1c02a6cf115c8d8f296675bec648 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at aac66a8 R-maint-sig mass rebuild