Update merge-main-into-prs.yml

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Updated the workflow for merging the main branch into open pull requests in the Ultralytics YOLO repository.

📊 Key Changes

• Branch Naming: Replaced hard-coded branch names (main, master) with a dynamic default branch reference.
• Python Version: Updated the workflow to use any 3.x Python version instead of specifically Python 3.11.
• Enhanced Logging: Added more detailed logging for the merge process, including success and failure messages.
• Environment Variables: Improved handling of GitHub token for authentication.

🎯 Purpose & Impact

• Flexibility: This change accommodates repositories with different default branch names, making the workflow more adaptable.
• Reliability: Using any 3.x Python version ensures broader compatibility without strictly tying to a single version.
• Transparency: Enhanced logging provides clearer insights into the merge process, helping developers understand the status and any issues.
• Security: Improved token handling enhances the security of the workflow by ensuring authentication is more robust.