### CI Link

only saw it locally

### Repro line

./gradlew ':server:test' --tests "org.elasticsearch.index.mapper.flattened.FlattenedFieldSearchTests.testCardinalityAggregation" -Dtests.seed=6E5A7D9AA8064CD5 -Dtests.locale=sr -Dtests.timezone=America/Campo_Grande -Druntime.java=18

### Does it reproduce?

Yes

### Applicable branches

master

### Failure history

_No response_

### Failure excerpt

```
REPRODUCE WITH: ./gradlew ':server:test' --tests "org.elasticsearch.index.mapper.flattened.FlattenedFieldSearchTests.testCardinalityAggregation" -Dtests.seed=EC78A8CA6F57105F -Dtests.locale=sv -Dtests.timezone=SystemV/MST7MDT -Druntime.java=18
  java.lang.AssertionError: 
    Expected: a value greater than <0L>
         but: <0L> was equal to <0L>
        at __randomizedtesting.SeedInfo.seed([EC78A8CA6F57105F:85146484AA481FC8]:0)
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
        at org.junit.Assert.assertThat(Assert.java:956)
        at org.junit.Assert.assertThat(Assert.java:923)
        at org.elasticsearch.index.mapper.flattened.FlattenedFieldSearchTests.assertCardinality(FlattenedFieldSearchTests.java:275)
        at org.elasticsearch.index.mapper.flattened.FlattenedFieldSearchTests.testCardinalityAggregation(FlattenedFieldSearchTests.java:249)
```

Reproduces every time for me locally. Will mute.

server/src/test/java/org/elasticsearch/index/mapper/flattened/FlattenedFieldSearchTests.java
client().prepareIndex()
                    .setSource(
                        XContentFactory.jsonBuilder()
                            .startObject()
                            .startObject("flattened")
                            .field("first", i)
                            .field("second", i / 2)
                            .endObject()
                            .endObject()
                    )
            );
        }
        for (int i = 0; i < 10; i++) {
            bulkRequest.add(client().prepareIndex("test").setSource("other_field", "1"));
        }
        BulkResponse bulkResponse = bulkRequest.get();
        assertNoFailures(bulkResponse);
        
        SearchResponse response = client().prepareSearch("test")
            .addAggregation(cardinality("cardinality").precisionThreshold(precisionThreshold).field("flattened"))
            .get();
        assertSearchResponse(response);
        Cardinality count = response.getAggregations().get("cardinality");
        assertCardinality(count, numDocs, precisionThreshold);
        
        SearchResponse firstResponse = client().prepareSearch("test")
            .addAggregation(cardinality("cardinality").precisionThreshold(precisionThreshold).field("flattened.first"))
            .get();
        assertSearchResponse(firstResponse);
        Cardinality firstCount = firstResponse.getAggregations().get("cardinality");