Fix test for parse of search failures

ShardSearchFailure.toXContent did not generate the outer level object,
fixed test to add this.

Related to backport of #42928

modules/reindex/src/test/java/org/elasticsearch/index/reindex/remote/RemoteResponseParsersTests.java

@@ -41,7 +41,9 @@ public class RemoteResponseParsersTests extends ESTestCase {
     public void testFailureWithoutIndex() throws IOException {
         ShardSearchFailure failure = new ShardSearchFailure(new EsRejectedExecutionException("exhausted"));
         XContentBuilder builder = jsonBuilder();
+        builder.startObject();
         failure.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        builder.endObject();
         try (XContentParser parser = createParser(builder)) {
             ScrollableHitSource.SearchFailure parsed = RemoteResponseParsers.SEARCH_FAILURE_PARSER.parse(parser, XContentType.JSON);
             assertNotNull(parsed.getReason());