Reconfigure/fix codecov so it's not spuriously red

[itamarst]

Whatever codecov/patch CI job is doing now, CI often ends up marked red despite everything passing and coverage not decreasing.

[itamarst]

One problem is that monkeypatching code is not run in the test process, it's tested via subprocesses. So possibly making sure subprocesses in tests get coverage too will fix most of it.

[itamarst]

Given the above, this is probably not as high a priority.

[itamarst]

#836 might fix the subprocess issue, it's possible pytest-cov makes this work automatically.

[4383]

Given the above, this is probably not as high a priority.

Yeah not a priority...