$ git clone -n https://src.fedoraproject.org/rpms/rubygem-open4.git /var/lib/mock/f40-build-2215262-52419/root/chroot_tmpdir/scmroot/rubygem-open4
Cloning into '/var/lib/mock/f40-build-2215262-52419/root/chroot_tmpdir/scmroot/rubygem-open4'...
$ git fetch origin a727b2944bd5507a0cca9da0f66446154e02c9f8:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-open4
 * [new ref]         a727b2944bd5507a0cca9da0f66446154e02c9f8 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a727b29 Use recent gem2rpm spec style