Owner can get added as reviewer, for legacy reasons. This happens when
owner votes on a label or submits a change. We already have code that
ensured that on submit the person who was added as reviewer doesn't get
added to the attention set (could be not the owner). However, we didn't
cover the case where the owner votes on push, hence adding themselves as
a reviewer.
Add a test case for this and ensure owner is not added to the attention
set when added as reviewer.
Bug: Issue 13770
Change-Id: Iee138b1064e70e8584f24e6b9d1b3e06a8a419c4
925bc8bdc6