### 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
}
    public void testExists() throws Exception {
        client().prepareIndex("test")
            .setId("1")
            .setRefreshPolicy(RefreshPolicy.IMMEDIATE)
            .setSource(
                XContentFactory.jsonBuilder()
                    .startObject()
                    .startObject("headers")
                    .field("content-type", "application/json")
                    .endObject()
                    .endObject()
            )
            .get();
        SearchResponse searchResponse = client().prepareSearch().setQuery(existsQuery("headers")).get();
        assertHitCount(searchResponse, 1L);
        searchResponse = client().prepareSearch().setQuery(existsQuery("headers.content-type")).get();
        assertHitCount(searchResponse, 1L);
        searchResponse = client().prepareSearch().setQuery(existsQuery("headers.nonexistent")).get();
        assertHitCount(searchResponse, 0L);
    }
    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/86115")
    public void testCardinalityAggregation() throws IOException {
        int numDocs = randomIntBetween(2, 100);
        int precisionThreshold = randomIntBetween(0, 1 << randomInt(20));
        BulkRequestBuilder bulkRequest = client().prepareBulk("test").setRefreshPolicy(RefreshPolicy.IMMEDIATE);
        
        
        for (int i = 0; i < numDocs; ++i) {
            bulkRequest.add(