We had placed our pytest configuration in setup.cfg, which is pretty

common, but deprecated. This isn't really a major problem in practice

for pytest itself (it's been deprecated for over 5 years yet still

supported), but the recent addition to the log format configuration

actually broke building packages on Python 2.7, as the format strings

could not be expanded to anything.
There are two places this could conceivably live: pytest.ini or

pyproject.toml. pyproject.toml is increasingly the future of

Python package configuration, but unsupported by pytest prior to 6.0,

which means we can't use it for Python 2.7.
So this change moves the configuration into pytest.ini instead. This

is universally supported and has highest precedence.

Successfully ran pytest on all supported versions of Python.
Successfully built packages.