$ git clone -n https://src.fedoraproject.org/rpms/rust-gengo.git /var/lib/mock/f42-build-side-1-3585571-46906/root/chroot_tmpdir/scmroot/rust-gengo
Cloning into '/var/lib/mock/f42-build-side-1-3585571-46906/root/chroot_tmpdir/scmroot/rust-gengo'...
$ git fetch origin 5481bc5e3a027ccb8336807d5ea3c1282bb809a2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-gengo
 * [new ref]         5481bc5e3a027ccb8336807d5ea3c1282bb809a2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5481bc5 Update to version 0.13.1; Fixes RHBZ#2378677