return early for fake communication channels
return early for fake communication channels

when processing our bounce_for_path we are trying to check thousands of
shards to do work against a user that is fake.

Still allowing permanent bounces to process because we actually stop
sending mail to those.

Change-Id: Ifcbe1a5f81bf69e8c6bcf19310bd522291d3e56c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/259630
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Product-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms