$ git clone -n https://src.fedoraproject.org/rpms/rust-grep.git /var/lib/mock/f40-build-2270960-54870/root/chroot_tmpdir/scmroot/rust-grep
Cloning into '/var/lib/mock/f40-build-2270960-54870/root/chroot_tmpdir/scmroot/rust-grep'...
$ git fetch origin 9034fe86256e91618dd8c01b0ee1e801143b9b95:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-grep
 * [new ref]         9034fe86256e91618dd8c01b0ee1e801143b9b95 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 9034fe8 Update to version 0.3.1; Fixes RHBZ#2251596