$ git clone -n https://src.fedoraproject.org/rpms/rubygem-rack-cache.git /var/lib/mock/f39-build-1499299-34744/root/chroot_tmpdir/scmroot/rubygem-rack-cache
Cloning into '/var/lib/mock/f39-build-1499299-34744/root/chroot_tmpdir/scmroot/rubygem-rack-cache'...
$ git fetch origin bc8e16a4d0099b5eb17f7a54345f744fd464f22d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-rack-cache
 * [new ref]         bc8e16a4d0099b5eb17f7a54345f744fd464f22d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at bc8e16a Updated to rack-cache 1.14.0.