$ git clone -n https://src.fedoraproject.org/rpms/Rex.git /var/lib/mock/f41-build-side-1-3129352-39577/root/chroot_tmpdir/scmroot/Rex
Cloning into '/var/lib/mock/f41-build-side-1-3129352-39577/root/chroot_tmpdir/scmroot/Rex'...
$ git fetch origin f068074a38ee04cb5b53adc866fdfa13ef68a06a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/Rex
 * [new ref]         f068074a38ee04cb5b53adc866fdfa13ef68a06a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f068074 Update to 1.15.0 (#2323989)