Require python >= 3.9

[youtux]

🤔 What's changed?

Python 3.8 is EOL, and the latest python is 3.13, so let's update the package metadata and the required python version to match that. We are testing already against python 3.9..3.13 anyway

⚡️ What's your motivation?

Keeping the codebase in sync with the latest supported python versions.

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)

♻️ Anything particular you want feedback on?

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[luke-hill]

This feels like a good thing to sync up with the C/Cpp changes which are also seemingly like breaking changes. Although the quantity of releases in gherkin they're nearly always breaking changes 😅