Fix incorrect `include` declarations with Poetry

[mgorny]

Fix the include declarations in pyproject.toml to be restricted to the sdist format. Otherwise, all the listed files are installed straight into site-packages, i.e. you get:

/usr/lib/python3.10/site-packages/CONTRIBUTING.md
/usr/lib/python3.10/site-packages/CHANGELOG.rst
...

[mgorny]

Ping. Over a year later, this is still broken.

[cdce8p]

Not sure this is an issue. The default for include is only sdist. https://python-poetry.org/docs/pyproject/#exclude-and-include

[mgorny]

Indeed, the default changed in poetry-core==2.0.0.