$ git clone -n https://src.fedoraproject.org/rpms/rust-cargo-readme.git /var/lib/mock/f39-build-1561742-37406/root/chroot_tmpdir/scmroot/rust-cargo-readme
Cloning into '/var/lib/mock/f39-build-1561742-37406/root/chroot_tmpdir/scmroot/rust-cargo-readme'...
$ git fetch origin 54d54bed78845b940882dd5cc4b9ce2ea680be03:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-cargo-readme
 * [new ref]         54d54bed78845b940882dd5cc4b9ce2ea680be03 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 54d54be Update to version 3.3.0; Fixes RHBZ#2237542