Update greetings.yml

[glenn-jocher]

Splash update for YOLOv5.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Updated welcome message image in the GitHub greetings workflow.

📊 Key Changes

• The welcome message for new contributors now includes a new image.
• Image source changed from a user content URL to a release asset URL in the repository.

🎯 Purpose & Impact

• 🖼️ Visual Refresh: The updated image in the welcome message may provide a more current and polished look, contributing to better first impressions.
• 🔗 Reliable Linking: Using a release asset URL for the image ensures it is directly tied to the repository's assets, potentially reducing the risk of the image link breaking in the future.
• 👥 User Experience: New contributors will be greeted with relevant and up-to-date visual information, possibly enhancing engagement and interest in the project.