Don't filter comments by actor

[luketomlinson]

Describe your issue

Right now, stale will determine if an issue has been updated by checking for comments that were not made by a bot and comments that were not made by the actor. The "actor" is somewhat opaque and can sometimes mean "the person who initiated the run" or the "actions bot". Rather than rely on this, we should check for comments that are equal to the stale message.

Further context