fix: [compose-core] use ``return 1`` instead of ``exit 1`` in ``_get_container_relation()``

bin/compose-core

@@ -3034,8 +3034,9 @@ _get_container_relation() {
         }
     done < <(_get_charm_metadata_uses "$metadata")
     if [ -z "$found" ]; then
-        die "Charm $DARKPINK$charm$NORMAL is a subordinate but does not have any required relation declaration with" \
+        err "Charm $DARKPINK$charm$NORMAL is a subordinate but does not have any required relation declaration with" \
             "${WHITE}scope${NORMAL} set to 'container'."
+        return 1
     fi
     printf "%s" "$found"
 }