Drop support for EOL Python 3.8

[hugovk]

Python 3.8 reached EOL in October 2024:

• https://devguide.python.org/versions/
• https://peps.python.org/pep-0569/

[hugovk]

I didn't change anything in the config below, except for these section renamings advised by ruff:

warning: The top-level linter settings are deprecated in favour of their counterparts in the `lint` section. Please update the following options in `pyproject.toml`:
  - 'ignore' -> 'lint.ignore'
  - 'select' -> 'lint.select'
  - 'isort' -> 'lint.isort'
  - 'per-file-ignores' -> 'lint.per-file-ignores'

And then the formatter re-ordered the sections.

Ruff also gave this warning, but I've not done anything about it, but can do if you like:

warning: The following rules may cause conflicts when used with the formatter: COM812, ISC001. To avoid unexpected behavior, we recommend disabling these rules, either by removing them from the select or extend-select configuration, or adding them to the ignore configuration.