message: integration_tests: fix warning on Windows
diff: @@ -23,6 +23,7 @@ protected:
  // We need to wait a bit until it's up and running.
  std::this_thread::sleep_for(std::chrono::seconds(10));
  #else
  + UNUSED(model);
  mavsdk::LogErr() << "Auto-starting SITL not supported on Windows.";
  #endif
  }
  