Infrastructure: Support rate-limit retries in link-checker

[howard-e]

From #3264 (comment):

A string of failures on this makes me think this solution is flaky in other areas, particularly with GitHub links. So something to investigate separately as well. 6 failures after my last commit for the following links:

• https://github.com/w3c/aria-practices/blob/main/.github/workflows/coverage-report.yml (x3)
• https://github.com/w3c/aria-practices/blob/main/scripts/coverage-report.js (x3)
• https://ainspector.disability.illinois.edu/

expand for list of failing builds

1. https://github.com/w3c/aria-practices/actions/runs/15139538651/job/42559608538?pr=3264
2. https://github.com/w3c/aria-practices/actions/runs/15139538651/job/42559779924?pr=3264
3. https://github.com/w3c/aria-practices/actions/runs/15139538651/job/42560052280?pr=3264
4. https://github.com/w3c/aria-practices/actions/runs/15139538651/job/42560300319?pr=3264
5. https://github.com/w3c/aria-practices/actions/runs/15139538651/job/42560518354?pr=3264
6. https://github.com/w3c/aria-practices/actions/runs/15139538651/job/42560823761?pr=3264

Originally posted by @howard-e in #3264 (comment)

Looking again at the responses, the response codes were 429 and an outlier 508 (which was still most likely related to rate limiting).

About this PR:

Since calls to external links are coming from an unauthenticated source, unable to parse out any reliable retry-related headers from the responses and even if, the links in this project are variable enough that, that may prove difficult to normalise. So defaulting to 15 seconds.

Note: Harder to confirm this on my local setup (but possible). Leaving as a draft while I confirm using this PR.

---

WAI Preview Link (Last built on Wed, 21 May 2025 22:13:40 GMT).

[howard-e]

For reviewers: this has now been re-ran 5 times without any unexpected failures to the link-checker build

[jugglinmike]

Does the formula for the delay in this case need to be different than the formula for the delay in case of an exception? If not, then we could reduce duplication by simply throwing here.

[howard-e]

Good point, de-duped and also removed left-over retry logic in e08b32c

[jugglinmike]

Looking good, @howard-e! I'd love to merge this for you, but GitHub feels differently:

Merging is blocked

You're not authorized to push to this branch. Visit https://docs.github.com/repositories/configuring-branches-and-merges-in-your-repository/managing-protected-branches/about-protected-branches for more information.

[howard-e]

Looking good, @howard-e! I'd love to merge this for you, but GitHub feels differently:

Merging is blocked
You're not authorized to push to this branch. Visit https://docs.github.com/repositories/configuring-branches-and-merges-in-your-repository/managing-protected-branches/about-protected-branches for more information.

Thanks! (and thinking we should look into your permissions here)