[CI] Failure in org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT

[original-brownbear]

An assertion added in #48815 is tripping in https://gradle-enterprise.elastic.co/s/el42prl447wfk/console-log#L5228

It's this one:

    GetFieldMappingsResponse(StreamInput in) throws IOException {
        super(in);
        int size = in.readVInt();
        Map<String, Map<String, FieldMappingMetaData>> indexMapBuilder = new HashMap<>(size);
        for (int i = 0; i < size; i++) {
            String index = in.readString();
            if (in.getVersion().before(Version.V_8_0_0)) {
                int typesSize = in.readVInt();
                assert typesSize == 1; // <--- trips

[elasticmachine]

Pinging @elastic/es-core-features (:Core/Features/Indices APIs)

[romseygeek]

Should be assert typesSize == 0 || typesSize == 1 - I'll open a PR, thanks @original-brownbear

[elasticmachine]

Pinging @elastic/es-search (:Search/Mapping)