$ git clone -n https://src.fedoraproject.org/rpms/guile-reader.git /var/lib/mock/f40-build-759258-120371/root/chroot_tmpdir/scmroot/guile-reader
Cloning into '/var/lib/mock/f40-build-759258-120371/root/chroot_tmpdir/scmroot/guile-reader'...
$ git fetch origin b1bacf474f3e0c008398d245dcb091304a8508a5:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/guile-reader
 * [new ref]         b1bacf474f3e0c008398d245dcb091304a8508a5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b1bacf4 Initial import (fedora#2218044)