x/build/cmd/gerritbot: Gobot shouldn't be added as a CC/Reviewer

Gobot is added as a CC when it says "Trybots beginning", and as a Reviewer when it posts Trybot-Result+1 or Trybot-Result-1. For example, see: https://go-review.googlesource.com/c/go/+/100475

I realise that this is how Gerrit is supposed to work for humans - a user should be subscribed to updates if they comment, and added as a reviewer if they touch one of the flags/labels. However, I think this is noisy for bots. Is there a way to keep it from happening?