[michisec]

This pull request improves support and error handling for posting comments on pull requests, especially those originating from forks, and enhances test coverage and documentation. The most important changes are summarized below.

Error handling and messaging for fork pull requests:

• Added a new APIError type and IsForbidden helper to detect GitHub API 403 errors, which typically occur when attempting to comment on pull requests from forks with a read-only token. The action now logs a clear warning and provides guidance on how to enable commenting (e.g., using pull_request_target or a write-capable token). [1] [2]
• Updated the README with a new section explaining why comments may fail on fork PRs, how to resolve this, and security considerations when using pull_request_target.

Comment handling improvements:

• Removed the maxCommentPages limit and updated the comment search logic to scan all pages, preventing duplicate comments when a pull request has many comments. [1] [2]

Testing enhancements:

• Added tests to verify that all comment pages are searched before creating a new comment and that the action logs the correct warning when a forbidden error occurs. [1] [2] [3]

Codebase maintenance:

• Minor code improvements, such as new imports to support testing and refactoring for clarity.

Documentation updates:

• Removed outdated v2 changelog information from the README to keep documentation current.