Ignore some errors when checking links

We are currently seeing the link checking workflow fail on transient errors. So
we should tell lychee to accept a wider range of responses, such as server
errors and timeouts, as these don't indicate a broken link, but are instead
temporary issues that we don't need to act upon.

.github/workflows/check_links.yml

@@ -42,5 +42,7 @@ jobs:
       - name: Check links
         uses: lycheeverse/lychee-action@7cd0af4c74a61395d455af97419279d86aafaede  # v2.0.2
         with:
-          args: "--exclude-all-private --include-verbatim --max-concurrency 24 --require-https --verbose --no-progress --timeout 60 './docs/**/*.md' './docs/**/*.html' './imported_docs/**/*.md' './imported_docs/**/*.html' --exclude-path './docs/ehrql/includes/generated_docs'"
+          args: "--exclude-all-private --include-verbatim --max-concurrency 24 --require-https --verbose --no-progress
+          --accept 200..=204, 429, 500..=511
+          --timeout 60 './docs/**/*.md' './docs/**/*.html' './imported_docs/**/*.md' './imported_docs/**/*.html' --exclude-path './docs/ehrql/includes/generated_docs'"
           token: ${{secrets.GITHUB_TOKEN}}