Update summarize_release.py

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improved issue labeling and release note summarization by refining code handling and adding merge date tracking.

📊 Key Changes

• 🏷️ Refined issue event content extraction by simplifying file opening.
• 📅 Added merge date tracking for pull requests in release summaries.
• 🚀 Sorted pull requests by merge date for better organization in summaries.
• 📝 Adjusted how current PR is identified in the summary generation script.
• 📄 Simplified file handling in markdown processing scripts.

🎯 Purpose & Impact

• 🛠️ Improved Code Maintenance: Simplifies code handling and readability, making it easier for developers to maintain.
• 📅 Enhanced Release Notes: Sorting PRs by merge date creates a clearer and more chronological release summary.
• 🚀 Better Organization: Users get a more intuitive and organized view of pull requests, making change tracking more efficient.