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
CountDownLatch latch = new CountDownLatch(1);
        indexShard.getThreadPool().executor(ThreadPool.Names.SEARCH).execute(() -> {
            try {
                for (int i = 0; i < numContexts; i++) {
                    ShardSearchRequest request = new ShardSearchRequest(
                        OriginalIndices.NONE,
                        new SearchRequest().allowPartialSearchResults(true),
                        indexShard.shardId(),
                        0,
                        1,
                        AliasFilter.EMPTY,
                        1.0f,
                        -1,
                        null
                    );
                    final ReaderContext context = searchService.createAndPutReaderContext(
                        request,
                        indexService,
                        indexShard,
                        indexShard.acquireSearcherSupplier(),
                        SearchService.KEEPALIVE_INTERVAL_SETTING.get(Settings.EMPTY).millis()
                    );
                    assertThat(context.id().getId(), equalTo((long) (i + 1)));
                    contextIds.add(context.id());
                }
                assertThat(searchService.getActiveContexts(), equalTo(contextIds.size()));
                while (contextIds.isEmpty() == false) {
                    final ShardSearchContextId contextId = randomFrom(contextIds);
                    assertFalse(searchService.freeReaderContext(new ShardSearchContextId(UUIDs.randomBase64UUID(), contextId.getId())));
                    assertThat(searchService.getActiveContexts(), equalTo(contextIds.size()));