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/test/java/org/elasticsearch/indices/SystemIndexMappingUpdateServiceTests.java
.setIndexFormat(6)
            .setVersionMetaKey("version")
            .setOrigin("FAKE_ORIGIN")
            .build();
        SystemIndexDescriptor d2 = SystemIndexDescriptor.builder()
            .setIndexPattern(".bar-*")
            .setPrimaryIndex(".bar-1")
            .setMappings(getMappings())
            .setSettings(getSettings())
            .setIndexFormat(6)
            .setVersionMetaKey("version")
            .setOrigin("FAKE_ORIGIN")
            .build();
        SystemIndices systemIndices = new SystemIndices(
            List.of(
                new SystemIndices.Feature("index 1", "index 1 feature", List.of(d1)),
                new SystemIndices.Feature("index 2", "index 2 feature", List.of(d2))
            )
        );
        ;
        SystemIndexMappingUpdateService manager = new SystemIndexMappingUpdateService(systemIndices, client);
        final List<SystemIndexDescriptor> eligibleDescriptors = manager.getEligibleDescriptors(
            Metadata.builder().put(getIndexMetadata(d2, d2.getMappings(), 6, IndexMetadata.State.OPEN)).build()
        );
        assertThat(eligibleDescriptors, hasSize(1));
        assertThat(eligibleDescriptors, contains(d2));
    }
    /**
     * Check that the manager won't try to upgrade closed indices.
     */