Codecov lets us specify [how much of a coverage drop is acceptable](https://docs.codecov.io/docs/commit-status#section-threshold). Since we are seeing some [PRs fail by just adding an extra comment line](https://github.com/python/cpython/pull/20), we should probably set a threshold of some sort to say a slight drop is acceptable. I'm thinking maybe 0.01% is okay? And the [configuration can be validated](https://docs.codecov.io/docs/codecov-yaml#section-validate-your-repository-yaml).