Also add ~bug in case it doesn't have ~bug

Here we can see that the bot first runs with Ask adding `regression:xx.x` for ~regression and add auto updated, but it doesn't bother to add ~bug and then the other rule Label missed ~bug for ~regression could come in and add ~bug.

https://gitlab.com/gitlab-org/gitlab-ce/issues/36704#note_95043919

Let's just label ~bug while we're at it.

@markglenfletcher Please review? Thanks!