Don't assign reviewer until CI has passed

[Danwhy]

Currently dwylbot can both assign people to review PRs, and alert you when your CI has passed. Would it be possible for dwylbot to only assign the reviewer to the pull request once the CI has passed?

This way, the person opening the PR can add an awaiting review label and request a review, then not have to worry about coming back to check that the CI has passed before assigning. This would save time for the person opening the PR, allowing them to get back to work straight away, and means the reviewer won't get alerted to review a failing build.

[ghost]

@Danwhy thanks for the suggestion! I imagine this is probably possible... @SimonLab / @naazy to confirm