$ git clone -n https://src.fedoraproject.org/rpms/rust-boxcar.git /var/lib/mock/f41-build-side-2-python-2710023-30481/root/chroot_tmpdir/scmroot/rust-boxcar
Cloning into '/var/lib/mock/f41-build-side-2-python-2710023-30481/root/chroot_tmpdir/scmroot/rust-boxcar'...
$ git fetch origin fbd01dcdd31a328e78f33fdd017469e7c61daa88:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-boxcar
 * [new ref]         fbd01dcdd31a328e78f33fdd017469e7c61daa88 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at fbd01dc Initial package (close RHBZ#2304023)