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
public void onResponse(SearchPhaseResult result) {
                    try {
                        
                        assertSame(Thread.currentThread(), currentThread);
                        assertThat(result, instanceOf(QuerySearchResult.class));
                        assertTrue(result.queryResult().isNull());
                    } finally {
                        latch.countDown();
                    }
                }
                @Override
                public void onFailure(Exception e) {
                    try {
                        throw new AssertionError(e);
                    } finally {
                        latch.countDown();
                    }
                }
            });
            latch.await();
        }
    }
    public void testDeleteIndexWhileSearch() throws Exception {
        createIndex("test");
        int numDocs = randomIntBetween(1, 20);
        for (int i = 0; i < numDocs; i++) {
            client().prepareIndex("test").setSource("f", "v").get();
        }
        indicesAdmin().prepareRefresh("test").get();
        AtomicBoolean stopped = new AtomicBoolean(false);