SearchServiceTests.testIsParallelCollectionSupportedForResults fails intermittently

```
12:37:10 org.elasticsearch.search.SearchServiceTests > testIsParallelCollectionSupportedForResults FAILED
12:37:10     java.lang.AssertionError
12:37:10         at __randomizedtesting.SeedInfo.seed([4140C168DE8FB0BB:771A78D5E4B36180]:0)
12:37:10         at org.junit.Assert.fail(Assert.java:86)
12:37:10         at org.junit.Assert.assertTrue(Assert.java:41)
12:37:10         at org.junit.Assert.assertFalse(Assert.java:64)
12:37:10         at org.junit.Assert.assertFalse(Assert.java:74)
12:37:10         at org.elasticsearch.search.SearchServiceTests.testIsParallelCollectionSupportedForResults(SearchServiceTests.java:2096)
```

```
./gradlew ':server:test' --tests "org.elasticsearch.search.SearchServiceTests.testIsParallelCollectionSupportedForResults" -Dtests.seed=4140C168DE8FB0BB -Dtests.locale=es-SV -Dtests.timezone=Africa/Banjul -Druntime.java=20
```
server/src/test/java/org/elasticsearch/search/SearchServiceTests.java
indexShard.shardId(),
            0,
            indexService.numberOfShards(),
            AliasFilter.EMPTY,
            1f,
            System.currentTimeMillis(),
            null
        );
        int executorPoolSize = randomIntBetween(1, 100);
        ExecutorService threadPoolExecutor = EsExecutors.newFixed(
            "test",
            executorPoolSize,
            0,
            Thread::new,
            new ThreadContext(Settings.EMPTY),
            EsExecutors.TaskTrackingConfig.DO_NOT_TRACK
        );
        ExecutorService notThreadPoolExecutor = Executors.newWorkStealingPool();
        SearchService service = getInstanceFromNode(SearchService.class);
        {
            assertEquals(executorPoolSize, service.determineMaximumNumberOfSlices(threadPoolExecutor, request, ResultsType.DFS));
            assertEquals(1, service.determineMaximumNumberOfSlices(null, request, ResultsType.DFS));
            assertEquals(1, service.determineMaximumNumberOfSlices(threadPoolExecutor, request, ResultsType.QUERY));
            assertEquals(1, service.determineMaximumNumberOfSlices(notThreadPoolExecutor, request, ResultsType.DFS));
        }
        try {
            ClusterUpdateSettingsResponse response = client().admin()
                .cluster()
                .prepareUpdateSettings()
                .setPersistentSettings(Settings.builder().put(QUERY_PHASE_PARALLEL_COLLECTION_ENABLED.getKey(), true).build())