regression: retargeting to trunk never prompts to take the PR out of draft #131

When we sync, a branch in a stack has been merged into the trunk, the "children" of this branch will be retargeted to trunk. The PRs associated with these children will (unless there's been manual intervention) be in "draft" status; since they now target the trunk, they should be "ready for review."

I no longer see a prompt to mark such PRs as "ready for review." Mind you, we should only ever ask to do this once (no asking again on a subsequent sync), and only if the PR is currently in "draft" status.

This regression may have been introduced by #100.