CI: tests don't test "download and extract" installation ..

... which, *cough*, is the documented installation method

> 1. Review [Noteworthy Differences](https://mitogen.networkgenomics.com/ansible_detailed.html#noteworthy-differences).
> 2. Download and extract [mitogen-0.3.30.tar.gz](https://files.pythonhosted.org/packages/source/m/mitogen/mitogen-0.3.30.tar.gz).
>
> -- https://mitogen.networkgenomics.com/ansible_detailed.html#installation