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
"version",
            "stack",
            Version.CURRENT.minimumCompatibilityVersion(),
            Type.INTERNAL_MANAGED,
            List.of(),
            List.of(),
            null,
            false,
            false
        );
    }
    TestSystemIndexDescriptor(String name, String primaryName, boolean allowsTemplates) {
        super(
            name + "*",
            primaryName,
            "Test system index",
            getOldMappings(),
            SETTINGS,
            name,
            0,
            "version",
            "stack",
            Version.CURRENT.minimumCompatibilityVersion(),
            Type.INTERNAL_MANAGED,
            List.of(),
            List.of(),
            null,
            false,
            allowsTemplates
        );