$ git clone -n https://src.fedoraproject.org/rpms/rpy.git /var/lib/mock/f38-build-side-42-init-devel-767952-27746/root/chroot_tmpdir/scmroot/rpy
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-767952-27746/root/chroot_tmpdir/scmroot/rpy'...
$ git fetch origin b90c2bc48ca8730dab4e44ff22da64e2371ddf25:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rpy
 * [new ref]         b90c2bc48ca8730dab4e44ff22da64e2371ddf25 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b90c2bc 3.5.10