$ git clone -n https://src.fedoraproject.org/rpms/gn.git /var/lib/mock/f42-build-60988806-6587310/root/chroot_tmpdir/scmroot/gn
Cloning into '/var/lib/mock/f42-build-60988806-6587310/root/chroot_tmpdir/scmroot/gn'...
$ git fetch origin b589f6b8c12255892881545aecf058213848de1d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gn
 * [new ref]         b589f6b8c12255892881545aecf058213848de1d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b589f6b Update to version 2256