ci: use `ubuntu-24.04`

[mkniewallner]

PR Checklist

• [x] A description of the changes is added to the description of this PR.
• [ ] If there is a related issue, make sure it is linked to this PR.
• [ ] If you've fixed a bug or added code that should be tested, add tests!
• [ ] If you've added or modified a feature, documentation in docs is updated

Description of changes

ubuntu-24.04 is available in beta: https://github.blog/changelog/2024-05-14-github-hosted-runners-public-beta-of-ubuntu-24-04-is-now-available/