CMake: need the `coverage` package to be present for our Python coverage

[agarny]

For our Python coverage to be available, we don't only need the exclude-until-coverage-plugin Python package, but also the coverage one.

[hsorby]

The exclude-until-coverage-plugin requires coverage so we do only need exclude-until-coverage-plugin.

[agarny]

Damn, I should have put a bit more context as I can't imagine (then again, who knows?!) creating this issue if there wasn't a need for it... but granted, I have just did pip install exclude-until-coverage-plugin on a vanilla Python virtual environment and it also installed coverage, so... closing... 🙄🙂