$ git clone -n https://src.fedoraproject.org/rpms/rust-capnp-rpc.git /var/lib/mock/f39-build-2087736-50159/root/chroot_tmpdir/scmroot/rust-capnp-rpc
Cloning into '/var/lib/mock/f39-build-2087736-50159/root/chroot_tmpdir/scmroot/rust-capnp-rpc'...
$ git fetch origin 124a9e0d68c155ee79a694bab557e68fe5b4cf5d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-capnp-rpc
 * [new ref]         124a9e0d68c155ee79a694bab557e68fe5b4cf5d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 124a9e0 Update to version 0.18.0; Fixes RHBZ#2139858