In the status UI, previously we never stated when the last validation
occurred. As we have access to this data, we should tell the user when
the last validation of a commit associated with a PR happened. This
better supports users to know if their failure may be due to out of date
validation.

Additionally, in the case of GH PRs where we have logic to manage those
calls separately, we can now check if the PR is open. We use this to now
toggle whether the revalidation button will be usable and whether the
hCaptcha is injected.