$ git clone -n https://src.fedoraproject.org/rpms/R-biomaRt.git /var/lib/mock/f42-build-side-1-3500774-45971/root/chroot_tmpdir/scmroot/R-biomaRt
Cloning into '/var/lib/mock/f42-build-side-1-3500774-45971/root/chroot_tmpdir/scmroot/R-biomaRt'...
$ git fetch origin a206662b1da5d562b0bb6ef22c3d8e5f94a3f0e4:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-biomaRt
 * [new ref]         a206662b1da5d562b0bb6ef22c3d8e5f94a3f0e4 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a206662 R-maint-sig mass rebuild