$ git clone -n https://src.fedoraproject.org/rpms/rubygem-gdk3.git /var/lib/mock/f40-build-2679206-67929/root/chroot_tmpdir/scmroot/rubygem-gdk3
Cloning into '/var/lib/mock/f40-build-2679206-67929/root/chroot_tmpdir/scmroot/rubygem-gdk3'...
$ git fetch origin ef5649552b68c1aaea30ebc09b1f4e19807ce6cb:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-gdk3
 * [new ref]         ef5649552b68c1aaea30ebc09b1f4e19807ce6cb -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ef56495 4.2.2 entry