migrate from removed setuptools' test command

[stanislavlevin]

setup.py test is deprecated since setuptools 41.5.0:
https://setuptools.pypa.io/en/latest/history.html#v41-5-0

setuptools 72.0.0 removed support for deprecated setup.py test command:

https://setuptools.pypa.io/en/stable/history.html#v72-0-0

The test command has been removed. Users relying on ‘setup.py test’ will need
to migrate to another test runner or pin setuptools before this version.