$ git clone -n https://src.fedoraproject.org/rpms/gthumb.git /var/lib/mock/f40-build-788334-135103/root/chroot_tmpdir/scmroot/gthumb
Cloning into '/var/lib/mock/f40-build-788334-135103/root/chroot_tmpdir/scmroot/gthumb'...
$ git fetch origin 08f92820e621ce1a6f8f7a30cdd819fa1be17ae3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gthumb
 * [new ref]         08f92820e621ce1a6f8f7a30cdd819fa1be17ae3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 08f9282 Update to 3.12.5