BuildRequire six explicitly, for tests
It was previously brought in by packaging.
+ pytest-3 -v -k 'not test_pip_download'
ImportError while loading conftest '/builddir/build/BUILD/setuptools_scm-4.1.2/testing/conftest.py'.
testing/conftest.py:4: in <module>
import six
E ModuleNotFoundError: No module named 'six'