Add NCNN export test to ci.yaml

[glenn-jocher]

@kalenmike adds NCNN export test to HUB CI.

copilot:all

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced model export compatibility in Ultralytics CI workflow.

📊 Key Changes

• Added support for ncnn format to the list of model export formats.

🎯 Purpose & Impact

• Purpose: To enable users to export their models to an additional format (ncnn), which is widely used for deploying models on mobile and embedded devices.
• Impact: Users benefit from greater flexibility in deploying their trained models across various platforms, particularly those that require the ncnn format, thus expanding Ultralytics' usability in the AI community. 📱✨