Mute test CompletionSuggestionTests.testToReduce

Relates to elastic#19896

Author: ywelsch

core/src/test/java/org/elasticsearch/search/suggest/completion/CompletionSuggestionTests.java

@@ -32,6 +32,7 @@
 
 public class CompletionSuggestionTests extends ESTestCase {
 
+ @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/19896")
  public void testToReduce() throws Exception {
  List<Suggest.Suggestion<CompletionSuggestion.Entry>> shardSuggestions = new ArrayList<>();
  int nShards = randomIntBetween(1, 10);