If MergeBot times out waiting for a Jenkins job it may start another merge after timing without cancelling the job.

[jasonkuster]

It doesn't seem likely that MergeBot will be able to cancel the job (investigate if we can get a key from Infra anyway) but in this case we should really capture the SHA of the latest commit and ensure that it and the commit Jenkins are testing are the same. Jenkins code should probably be updated to handle this contingency.