$ git clone -n https://src.fedoraproject.org/rpms/rust-cxx-build.git /var/lib/mock/f41-build-side-1-2940046-35321/root/chroot_tmpdir/scmroot/rust-cxx-build
Cloning into '/var/lib/mock/f41-build-side-1-2940046-35321/root/chroot_tmpdir/scmroot/rust-cxx-build'...
$ git fetch origin 1fe2155fcc857523116b9e29fc0cbdcb1e893be1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-cxx-build
 * [new ref]         1fe2155fcc857523116b9e29fc0cbdcb1e893be1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 1fe2155 Update to version 1.0.128 (rhbz#2309028)