$ git clone -n https://src.fedoraproject.org/rpms/Rex.git /var/lib/mock/f40-build-2232495-53334/root/chroot_tmpdir/scmroot/Rex
Cloning into '/var/lib/mock/f40-build-2232495-53334/root/chroot_tmpdir/scmroot/Rex'...
$ git fetch origin 60a62e3402577e862e0e9916bffc92f24a80630b:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/Rex
 * [new ref]         60a62e3402577e862e0e9916bffc92f24a80630b -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 60a62e3 Improve the BuildRequires list