ci: retry link checker on failure to handle GitHub rate limits (#633)

GitHub rate-limits unauthenticated requests from CI runner IPs,
causing intermittent 403/429 on same-repo blob URLs. Retry only
the failed links (--lf) so transient rate limits pass on second
attempt while real broken links still fail.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: paddymul

.github/workflows/checks.yml

@@ -682,8 +682,8 @@ jobs:
           touch buckaroo/static/widget.js
           touch buckaroo/static/widget.css
           mkdir -p docs/build/html
-          uv run pytest --check-links docs/source/*.rst
-          uv run pytest --check-links docs/example-notebooks/*.ipynb
+          uv run pytest --check-links docs/source/*.rst || uv run pytest --check-links --lf docs/source/*.rst
+          uv run pytest --check-links docs/example-notebooks/*.ipynb || uv run pytest --check-links --lf docs/example-notebooks/*.ipynb
           uv run sphinx-build -T -b html docs/source docs/build
 
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