ci: codecov continues to report a drop in coverage #197
Description
Problem
See, for example #196. Due to the addition of test files, our codecov percentage went from 70% to 50%. This reduction is causing builds to fail, even after manual approval of the last few commits.
Proposed solution
Get codecov to view the current level of coverage as the new baseline, and only fail a build if coverage drops further. Not clear on the standards for this, but perhaps data files should not be included in the percentage if they will cause problems like this.