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

bin/compose-core

@@ -5526,19 +5526,17 @@ case "$action" in
         ;;
 esac
 
-if [ -n "$is_docker_compose_action_multi_service" ]; then
-    if [ -n "$DEBUG" ]; then
+if [ -n "$DEBUG" ]; then
     Elt "get relation subset"
     start=$(time_now)
-    fi
+fi
 
-    get_subset_relations "${services_args[@]}" >/dev/null || exit 1
+get_subset_relations "${services_args[@]}" >/dev/null || exit 1
 
-    if [ -n "$DEBUG" ]; then
+if [ -n "$DEBUG" ]; then
     elapsed="$(time_elapsed $start "$(time_now)")" || exit 1
     print_info "$(printf "%.3fs" "$elapsed")"
     Feedback
-    fi
 fi
 
 if [ -n "$is_docker_compose_action" ] && [ "${#services_args[@]}" -gt 0 ]; then