@Override
    public void onResignation(
        int groupMetadataPartitionIndex,
        OptionalInt groupMetadataPartitionLeaderEpoch
    ) {
        throwIfNotActive();
        runtime.scheduleUnloadOperation(
            new TopicPartition(Topic.GROUP_METADATA_TOPIC_NAME, groupMetadataPartitionIndex),
            groupMetadataPartitionLeaderEpoch
        );
    }
See {@link GroupCoordinator#onResignation(int, OptionalInt)}.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/GroupCoordinatorService.java