Serialize post-mlinter-review after post-link to avoid PR description race (#47832)

* Serialize post-mlinter-review after post-link to avoid PR description race

Both jobs patch the PR description; running them in parallel causes the
last writer to silently overwrite the other's changes. Adding
`needs: post-link` ensures post-mlinter-review reads the already-updated
description (with CI badge) before appending the mlinter state block.

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

* Add always() so post-mlinter-review runs even if post-link fails

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

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Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>