Update Python versions tested in CI

- Python 3.14 is added.
- Python 3.9 is dropped. PDM failed to install, probably because of
  a hidden version incompatibility. However, this is an outdated Python
  version we don't actually care about so much.

Author: dranjan

.github/workflows/python-package.yml

@@ -23,7 +23,7 @@ jobs:
         strategy:
             fail-fast: false
             matrix:
-                python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
+                python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
         steps:
         - uses: actions/checkout@v3
         - name: Set up Python ${{ matrix.python-version }}