$ git clone -n https://src.fedoraproject.org/rpms/rubygem-gio2.git /var/lib/mock/f40-build-796885-140979/root/chroot_tmpdir/scmroot/rubygem-gio2
Cloning into '/var/lib/mock/f40-build-796885-140979/root/chroot_tmpdir/scmroot/rubygem-gio2'...
$ git fetch origin 7cc59f66ebe922c2ccbf9e989e8e7ac983ba7187:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-gio2
 * [new ref]         7cc59f66ebe922c2ccbf9e989e8e7ac983ba7187 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 7cc59f6 4.2.1 entry