Investigate using checks events instead of pull request ones

I recall looking into this early on, when checks were still in beta, and it not working as desired. I should dig up slack history from the internal adobe channel to pull up details of the issues that were had, and see if we're still experiencing it.

If we can move away from PR events and instead rely on check events, then we can have the bot properly respond to "rerun check" UI interactions.

Review the bot's current pull request event handling and investigate GitHub check events, including the "rerun check" interaction. Search the internal Adobe Slack history for the earlier beta investigation and document whether the current limitations remain. Done means there is a clear decision on whether check events can replace the existing events and support reruns.

Written by the indexing model from the issue text.