Update checkout and setup-python to latest versions

Fix warnings about deprecated Node.js 16 actions.

See:

- #1493
- https://github.com/Kozea/Radicale/actions/runs/8943158465/attempts/1

.github/workflows/pypi-publish.yml

@@ -7,8 +7,8 @@ jobs:
   publish:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-python@v2
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
         with:
           python-version: 3.x
       - name: Install Build dependencies