### 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
.field("other_key", "D")
                    .endObject()
                    .endObject()
            )
            .get();
        client().prepareIndex("test")
            .setId("2")
            .setRefreshPolicy(RefreshPolicy.IMMEDIATE)
            .setSource(
                XContentFactory.jsonBuilder()
                    .startObject()
                    .startObject("flattened")
                    .field("key", "B")
                    .field("other_key", "C")
                    .endObject()
                    .endObject()
            )
            .get();
        client().prepareIndex("test")
            .setId("3")
            .setRefreshPolicy(RefreshPolicy.IMMEDIATE)
            .setSource(XContentFactory.jsonBuilder().startObject().startObject("flattened").field("other_key", "E").endObject().endObject())
            .get();
        SearchResponse response = client().prepareSearch("test").addSort("flattened", SortOrder.DESC).get();
        assertSearchResponse(response);
        assertHitCount(response, 3);
        assertOrderedSearchHits(response, "3", "1", "2");
        response = client().prepareSearch("test").addSort("flattened.key", SortOrder.DESC).get();
        assertSearchResponse(response);
        assertHitCount(response, 3);