upgrade release process from setup.py to most up-to-date way

[niccokunzmann]

Python 3.12 removes setuptools. It seems there is a new way forward using pyproject.toml. To close this issue, release this package according to the latest documentation: https://packaging.python.org/en/latest/guides/section-build-and-publish/

Files to touch:

• https://github.com/collective/icalendar/blob/main/.github/workflows/tests.yml
• https://github.com/collective/icalendar/blob/main/setup.py
• https://github.com/collective/icalendar/blob/main/docs/install.rst
• https://github.com/collective/icalendar/blob/main/docs/maintenance.rst

See also:

• 635

[niccokunzmann]

We published v6.0.0 with pyproject.toml and hatchling.