chore(ci): add informational Codecov status checks

[thomasrockhu-codecov]

Hi, Tom from Codecov here. I noticed that you were using Codecov but weren't actually getting any notifications on pull requests. I figured it would be useful to get some idea if code being changed is being tested, but also not blocking CI/merging. Let me know if this makes sense or if we can do something that would be helpful.