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
final int configuredMaxPoolSize = 10;
        executor.setMaximumPoolSize(configuredMaxPoolSize); 
        int numDocs = randomIntBetween(50, 100);
        for (int i = 0; i < numDocs; i++) {
            client().prepareIndex("index").setId(String.valueOf(i)).setSource("field", "value").get();
            if (i % 5 == 0) {
                indicesAdmin().prepareRefresh("index").get();
            }
        }
        final IndexShard indexShard = indexService.getShard(0);
        ShardSearchRequest request = new ShardSearchRequest(
            OriginalIndices.NONE,
            new SearchRequest().allowPartialSearchResults(randomBoolean()),
            indexShard.shardId(),
            0,
            indexService.numberOfShards(),
            AliasFilter.EMPTY,
            1f,
            System.currentTimeMillis(),
            null
        );
        SearchService service = getInstanceFromNode(SearchService.class);
        NonCountingTermQuery termQuery = new NonCountingTermQuery(new Term("field", "value"));
        assertEquals(0, executor.getCompletedTaskCount());
        try (ReaderContext readerContext = createReaderContext(indexService, indexShard)) {
            SearchShardTask task = new SearchShardTask(0, "type", "action", "description", null, emptyMap());
            {
                SearchContext searchContext = service.createContext(readerContext, request, task, ResultsType.DFS, true);
                ContextIndexSearcher searcher = searchContext.searcher();
                assertNotNull(searcher.getExecutor());