$ git clone -n https://src.fedoraproject.org/rpms/rust-tar.git /var/lib/mock/f39-build-1455652-32918/root/chroot_tmpdir/scmroot/rust-tar
Cloning into '/var/lib/mock/f39-build-1455652-32918/root/chroot_tmpdir/scmroot/rust-tar'...
$ git fetch origin d3e893d981aba4b50ae9a0740582f4eca15c9a65:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-tar
 * [new ref]         d3e893d981aba4b50ae9a0740582f4eca15c9a65 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at d3e893d Update to version 0.4.40; Fixes RHBZ#2229807