Automatically marking old incomplete check runs as `stale`

If a check run is in an incomplete state for more than 14 days, GitHub will automatically change the check run's conclusion to stale. The new stale state will be denoted with the symbol and behaves similarly to the timed_out and canceled conclusions. When GitHub marks a check run as stale, a check run webhook event is triggered.

This will prevent old incomplete check runs from stopping apps that rely on the completed check suite event to trigger a flow.

Only GitHub can mark check runs as stale. For more information about possible conclusions of a check run, see the conclusion parameter.

This new behavior will go into effect after February 26th, 2020. All incomplete check runs older than 14 days will be marked stale. This feature will roll out slowly over a couple of days.