Force COMMENT for PR review when reviewer is the PR author

[strawgate]

Fixes #15837

• Detects when the authenticated user submitting a PR review is also the PR author and automatically downgrades APPROVE or REQUEST_CHANGES to COMMENT
• GitHub API rejects non-COMMENT reviews on your own PRs, so this prevents a failed API call and preserves the review content

[Copilot]

Pull request overview

This PR implements a safeguard to prevent API errors when a reviewer attempts to approve or request changes on their own pull request. GitHub's API only allows COMMENT reviews on your own PRs, so this change automatically downgrades APPROVE or REQUEST_CHANGES events to COMMENT when the authenticated user is also the PR author.

Changes:

• Added author check in submitReview() that compares authenticated user with PR author before submitting
• Automatically downgrades non-COMMENT review events to COMMENT when reviewer equals PR author
• Added 6 comprehensive test cases covering all scenarios including edge cases and error handling

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
actions/setup/js/pr_review_buffer.cjs	Implements author detection logic using github.rest.users.getAuthenticated() with graceful error handling and optional chaining
actions/setup/js/pr_review_buffer.test.cjs	Adds comprehensive test coverage for author check including happy path, edge cases (missing user info), and error scenarios

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