Add sleep and retry when secondary rate limit impacts on PR search

[SeanTAllen]

We hit this error semi-regularly. GitHub's secondary rate limiting is easy to trigger. It often will happen if multiple requests to the API are made at the same time from different jobs resulting in a failure. The failure is easy to fix by rerunning the job, but a user has to notice.

There might be other places that we can hit a similar issue, but this commit addresses the known location.

Fixes #37

[ponylang-main]

Hi @SeanTAllen,

The changelog - added label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do.

Release notes are added by creating a uniquely named file in the .release-notes directory. We suggest you call the file 38.md to match the number of this pull request.

The basic format of the release notes (using markdown) should be:

## Title

End user description of changes, why it's important,
problems it solves etc.

If a breaking change, make sure to include 1 or more
examples what code would look like prior to this change
and how to update it to work after this change.

Thanks.