fix error status code in sniff test

Author: l-trotta

java-client/src/test/java/co/elastic/clients/transport/rest5_client/low_level/sniffer/ElasticsearchNodesSnifferTests.java

@@ -373,6 +373,6 @@ static SniffResponse buildResponse(String nodesInfoBody, List<Node> nodes) {
     }
 
     private static int randomErrorResponseCode() {
-        return randomIntBetween(400, 599);
+        return randomIntBetween(500, 599);
     }
 }