[schema] fix buggy composite_rdef_roles and associated test
it should only look at rdefs involving the considered entity type.
Closes #3712982
#! /bin/sh -e#if [ "$1" = configure ]; then if which install-docs >/dev/null 2>&1; then install-docs -i /usr/share/doc-base/cubicweb-doc fifi#DEBHELPER#exit 0