Add Python 3.15 support and drop Python 3.9 - #430

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Landlock ABI 10 or later is required to deny all network access; found ABI 7. Applying the network restrictions supported by this kernel.

python@3.10 has been deprecated because it is deprecated upstream! It will be disabled on 2027-10-01.