$ git clone -n https://src.fedoraproject.org/rpms/rust-git2.git /var/lib/mock/f40-build-2637415-66220/root/chroot_tmpdir/scmroot/rust-git2
Cloning into '/var/lib/mock/f40-build-2637415-66220/root/chroot_tmpdir/scmroot/rust-git2'...
$ git fetch origin 3029b073eaf2963167b960a243fbbfbd7fc67fff:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-git2
 * [new ref]         3029b073eaf2963167b960a243fbbfbd7fc67fff -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3029b07 Update to version 0.18.3; Fixes RHBZ#2270319