Periodically check for missed status updates

[Riscky]

Sometimes PRs gets stuck in the merge queue because Hoff missed the webhook that should have told it that CI passed.
There can be multiple reasons for the webhook to go missing: GitHub having issues, Hoffs webhook queue being full, etc.
Currently, the only way to get PRs that got stuck to merge, is to close and reopen the PR, then tag Hoff again.
Instead, it would be nice if Hoff could periodically check the GitHub API for the status of CI for each PR, and continue the merge even if it has missed a webhook.

[Riscky]

GitHub has an API to redeliver webhooks: https://docs.github.com/en/webhooks/using-webhooks/automatically-redelivering-failed-deliveries-for-a-github-app-webhook
Although that won't fix problems if Hoff crashes before handling a webhook that it acknowledged, nor help if GitHub is having problems with webhook delivery, it seems to be quite easy to implement