feat: Drop Python 3.8 support and add Python 3.13 tests

[bosd]

This commit drops support for Python 3.8, which was failing due to an issue with an older version of setuptools and the license field in pyproject.toml.

The supported Python version range is now '>=3.9'.

Additionally, this commit adds a test job for Python 3.13 to the CI workflow to ensure compatibility with the latest Python version.