fix: [compose-core] make charm action also compute relation subset

bin/compose-core

@@ -5526,7 +5526,6 @@ case "$action" in
         ;;
 esac
 
-if [ -n "$is_docker_compose_action_multi_service" ]; then
 if [ -n "$DEBUG" ]; then
     Elt "get relation subset"
     start=$(time_now)
@@ -5539,7 +5538,6 @@ if [ -n "$is_docker_compose_action_multi_service" ]; then
     print_info "$(printf "%.3fs" "$elapsed")"
     Feedback
 fi
-fi
 
 if [ -n "$is_docker_compose_action" ] && [ "${#services_args[@]}" -gt 0 ]; then
     services=($(get_master_services "${services_args[@]}")) || exit 1