tests: switch to `coverage run nose`

[igaw]

nose2 says:

 **********
WARNING
Support for the nose2 coverage plugin is gradually being removed. Use `coverage run nose` instead.

For more detail, see https://github.com/nose-devs/nose2/issues/651
**********

[igaw]

https://github.com/linux-nvme/nvmetcli/actions/runs/29335863014/job/87094805903?pr=13#step:3:552

Warning: you need to install "coverage_plugin" extra requirements to use this plugin. e.g. `pip install nose2[coverage_plugin]`
OK (skipped=2)