Add grouped updates smoke tests for yarn

[bdragon]

Adds smoke tests for yarn and makes some updates to existing smoke tests along the way.

There's a yarn berry workspaces project in this repo, which led me to think it was being used in the tests/smoke-yarn-berry-workspaces.yaml test, but in fact the test was actually running against another repo, https://github.com/dsp-testing/dependabot-core-6432. To avoid confusion, I updated the smoke test to use the workspaces project included in this repo (dependabot/smoke-tests).