$ git clone -n https://src.fedoraproject.org/rpms/boost1.78.git /var/lib/mock/f38-build-side-42-init-devel-836455-28395/root/chroot_tmpdir/scmroot/boost1.78
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-836455-28395/root/chroot_tmpdir/scmroot/boost1.78'...
$ git fetch origin cab47dd4552646f816a7726d1f9669f68d60b68a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/boost1.78
 * [new ref]         cab47dd4552646f816a7726d1f9669f68d60b68a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cab47dd Added the README