$ git clone -n https://src.fedoraproject.org/rpms/rust-capnp.git /var/lib/mock/f40-build-2081244-49751/root/chroot_tmpdir/scmroot/rust-capnp
Cloning into '/var/lib/mock/f40-build-2081244-49751/root/chroot_tmpdir/scmroot/rust-capnp'...
$ git fetch origin 4c9ffed12d66716d09f1edc328bf0b1611ee38e4:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-capnp
 * [new ref]         4c9ffed12d66716d09f1edc328bf0b1611ee38e4 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4c9ffed Update to version 0.18.10; Fixes RHBZ#2139859