$ git clone -n https://src.fedoraproject.org/rpms/rust-xml-rs.git /var/lib/mock/f40-build-1936772-25145/root/chroot_tmpdir/scmroot/rust-xml-rs
Cloning into '/var/lib/mock/f40-build-1936772-25145/root/chroot_tmpdir/scmroot/rust-xml-rs'...
$ git fetch origin b81b7e3a56d3ca7ee4fbffa66050bfbd84e99c25:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-xml-rs
 * [new ref]         b81b7e3a56d3ca7ee4fbffa66050bfbd84e99c25 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b81b7e3 Update to version 0.8.21; Fixes RHBZ#2302913