Various `BuildChooser` implementations in Git plugin creates additional commits beyond what's checked out from GitHub, such as Gerrit Trigger plugin or GitHub PR builders.

Today, such commit creates a commit status update to fail, which fails the entire build. This is clearly not desirable. As the user, my only choice is to remove the use of commit status updater altogether. As an user, this comes across as an example of "plugins not working together."

It'd be a fairly easy fix to fail more gracefully if the commit is not in GitHub. In a long run, it would be even better if such `BuildChooser`s could designate a commit to which the status update should be attached to.