[CI] Increase retries for 409 on Serverless tests

[picandocodigo]

This test still takes longer on Serverless, 20 retries worked for 9.0, so hopefully will work on main too. Error:

Test: machine_learning/20_trained_model_serverless.yml
Action: ["do", {"ml.infer_trained_model" => {"model_id" => "test_model", "body" => "{\n  \"docs\": [\n    { \"input\": \"words\" }\n  ]\n}\n"}}]
Hash - [409] {"error":{"root_cause":[{"type":"status_exception","reason":"Trained model deployment [test_model] is not allocated to any nodes"}],"type":"status_exception","reason":"Trained model deployment [test_model] is not allocated to any nodes"},"status":409}