Replace third-party comment action with actions/github-script

[devin-ai-integration]

Summary

Replaces the thollander/actions-comment-pull-request@v2.4.3 third-party action with GitHub's official actions/github-script@v7 for posting and updating PR comments in the preview-docs workflow.

The new implementation:

• Uses a hidden HTML marker (<!-- preview-docs-comment -->) to identify the preview comment
• Uses the Octokit API via github.rest.issues.listComments to find existing comments
• Updates the existing comment if found, otherwise creates a new one

Review & Testing Checklist for Human

• Test the workflow end-to-end: Create a test PR, push a commit, verify comment is created. Push another commit, verify the same comment is updated (not a new one created)
• Verify comment body handling: Test with MDX files that produce special characters or complex markdown in the diff output to ensure the comment body is properly handled
• Check for pagination edge case: If a PR has 100+ comments, listComments may not return all comments by default (though this is unlikely in practice)

Notes

Requested by: kenny

Link to Devin run: https://app.devin.ai/sessions/721831cc9aad445b8db89c07b4ff7bad

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[github-actions]

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