Retry requests that fail with transient HTTP errors

[jwodder]

Use https://docs.rs/reqwest-retry?

See GitHub's documentation on retrying with the REST API:

• https://docs.github.com/en/rest/guides/best-practices-for-using-the-rest-api?apiVersion=2022-11-28#dealing-with-rate-limits
• https://docs.github.com/en/rest/overview/resources-in-the-rest-api?apiVersion=2022-11-28#rate-limiting