CI: Remove ubuntu-kinetic (defunct)

[mkoeppe]

This non-LTS release can no longer be tested.

https://github.com/sagemath/sage/actions/runs/6207962004/job/16853655527#step:8:60

E: The repository 'http://security.ubuntu.com/ubuntu kinetic-security Release' does not have a Release file.
E: The repository 'http://archive.ubuntu.com/ubuntu kinetic Release' does not have a Release file.
E: The repository 'http://archive.ubuntu.com/ubuntu kinetic-updates Release' does not have a Release file.
E: The repository 'http://archive.ubuntu.com/ubuntu kinetic-backports Release' does not have a Release file.

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[dimpase]

lgtm

[github-actions]

Documentation preview for this PR (built with commit 6abcf56; changes) is ready! 🎉