Although the line about setuptools is used in a lot of our projects
it's not relevant to the example CI configuration in this repo.

This contains configuration that it's useful to include in the
pyproject.toml file of a project using this CI template. It sets some
things for the three tools the CI check runs to make them compatible
with one another.

The version of black/isort/flake8 matters more than the version of
Python. Use dates until we can decide on specific versions of those,
which will probably come after we use this seriously.

We need this to configure flake8 in pyproject.toml and therefore keep
all our config together.