dev/release: support reference clones for other repos

Created by: keegancsmith

The recent commit which added --reference-if-able assumed we always cloned sourcegraph/sourcegraph. However, commands such as "yarn release release:stage" clone the about repo. We didn't fail in those cases, but by adjusting how we pick the reference we will often get the same benefits.

Test Plan: dry run without main branch check then ran the release command.