$ git clone -n https://src.fedoraproject.org/rpms/rubygem-powerpack.git /var/lib/mock/f39-build-1499282-34744/root/chroot_tmpdir/scmroot/rubygem-powerpack
Cloning into '/var/lib/mock/f39-build-1499282-34744/root/chroot_tmpdir/scmroot/rubygem-powerpack'...
$ git fetch origin ef70211f6a2ae51922a53221d5dbdf0e125336a4:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-powerpack
 * [new ref]         ef70211f6a2ae51922a53221d5dbdf0e125336a4 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ef70211 update to new version