Fix mlinter artifact path (#48088)

* Fix mlinter artifact path and prevent duplicate inline comments

Pass explicit artifact directory to post_mlinter_review.py so it finds
the files downloaded by actions/download-artifact (which lands them in
runner.temp, not the CWD). Also deletes old review inline comments
before posting a new review to prevent accumulation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Fix mlinter artifact download path so post_mlinter_review.py finds it

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Fix mlinter artifact path and prevent duplicate inline comments

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Use env var instead of inline expression in run step

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Revert post_mlinter_review.py (script changes belong in verification PR)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>