The following aggregation tests all contain switch statements with branches that will never execute. The tests use a `between(x, y)` switch expression, but there are `case` values that are outside the randomised range. We need to fix these before #88739 can be merged. By "fix", I mean either remove the spurious cases, or if we actually want them, then extend the randomized range.

   * InternalAutoDateHistogramTests
   * InternalAvgTests
   * InternalDerivativeTests
   * InternalGeoCentroidTests
   * InternalWeightedAvgTests
   * SignificantLongTermsTests
   * SignificantStringTermsTests
server/src/test/java/org/elasticsearch/search/aggregations/bucket/histogram/InternalAutoDateHistogramTests.java
}
        assertThat(reduced.getInterval(), equalTo(expectedInterval));
    }
    private int getBucketCount(long min, long max, Rounding.Prepared prepared, int interval) {
        int bucketCount = 0;
        long key = prepared.round(min);
        while (key < max) {
            for (int i = 0; i < interval; i++) {
                key = prepared.nextRoundingValue(key);
            }
            bucketCount++;
        }
        return bucketCount;
    }
    @Override
    protected Class<ParsedAutoDateHistogram> implementationClass() {
        return ParsedAutoDateHistogram.class;
    }
    @Override
    protected InternalAutoDateHistogram mutateInstance(InternalAutoDateHistogram instance) {
        String name = instance.getName();
        List<InternalAutoDateHistogram.Bucket> buckets = instance.getBuckets();
        int targetBuckets = instance.getTargetBuckets();
        BucketInfo bucketInfo = instance.getBucketInfo();
        Map<String, Object> metadata = instance.getMetadata();
        long interval = instance.getBucketInnerInterval();
        switch (between(0, 3)) {
            case 0 -> name += randomAlphaOfLength(5);
            case 1 -> {
                buckets = new ArrayList<>(buckets);