$ git clone -n https://src.fedoraproject.org/rpms/rust-b3sum.git /var/lib/mock/f41-build-846644-163162/root/chroot_tmpdir/scmroot/rust-b3sum
Cloning into '/var/lib/mock/f41-build-846644-163162/root/chroot_tmpdir/scmroot/rust-b3sum'...
$ git fetch origin 7fe89a0fa7e1e0b842e4dc2eed24920083cc8d20:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-b3sum
 * [new ref]         7fe89a0fa7e1e0b842e4dc2eed24920083cc8d20 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 7fe89a0 Update to 1.5.4 (close RHBZ#2306015)