Update CHANGELOG with recent changes and additions

Updated the CHANGELOG to reflect recent additions and changes, including improvements to the inactivity-unassign bot and updates to the CustomFixedFee class.

Signed-off-by: Akshat8510 <akshat230405@gmail.com>

Author: Akshat8510

CHANGELOG.md

@@ -8,7 +8,7 @@ This changelog is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.
 
 ### Added
 - Phase 2 of the inactivity-unassign bot:Automatically detects stale open pull requests (no commit activity for 21+ days), comments with a helpful InactivityBot message, closes the stale PR, and unassigns the contributor from the linked issue.
-- Added __str__() to CustomFixedFee and updated examples and tests accordingly.
+- Added **str**() to CustomFixedFee and updated examples and tests accordingly.
 - Added a github template for good first issues
 - Added `.github/workflows/bot-assignment-check.yml` to limit non-maintainers to 2 concurrent issue assignments.
 - Added all missing fields to **str**() method and updated `test_tokem_info.py`