Once https://github.com/elastic/elasticsearch/issues/98503 is done, we can use our minimum version numbers in the SystemIndexMappingUpdate service instead of the old `Version` types. Mappings will be updated for a system index when all nodes have a matching descriptor mappings version for a system index, but this version is greater than what's stored in the mappings metadata.
server/src/internalClusterTest/java/org/elasticsearch/indices/TestSystemIndexDescriptor.java
}
    @Override
    public boolean isAutomaticallyManaged() {
        return true;
    }
    @Override
    public String getMappings() {
        return useNewMappings.get() ? getNewMappings() : getOldMappings();
    }
    public static String getOldMappings() {
        try {
            final XContentBuilder builder = jsonBuilder();
            builder.startObject();
            {
                builder.startObject("_meta");
                builder.field(SystemIndexDescriptor.VERSION_META_KEY, 0);
                builder.field("version", Version.CURRENT.previousMajor().toString());
                builder.endObject();
                builder.startObject("properties");
                {
                    builder.startObject("foo");
                    builder.field("type", "text");
                    builder.endObject();
                }
                builder.endObject();
            }
            builder.endObject();
            return Strings.toString(builder);
        } catch (IOException e) {
            throw new UncheckedIOException("Failed to build .test-index-1 index mappings", e);