CI: check yarn.lock for changes
Created by: chrismwendt
This should prevent a dirty yarn.lock from getting checked in, resulting in PRs to update it such as https://github.com/sourcegraph/sourcegraph/pull/5330
Created by: chrismwendt
This should prevent a dirty yarn.lock from getting checked in, resulting in PRs to update it such as https://github.com/sourcegraph/sourcegraph/pull/5330