Remove separate setup-python in workflow

Let setup-uv handle the Python version management. It seems to be
sufficiently efficient.

Author: rra

.github/workflows/ci.yaml

@@ -32,11 +32,6 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
-      - name: Set up Python
-        uses: actions/setup-python@v6
-        with:
-          python-version-file: ".python-version"
-
       - name: Install uv
         uses: astral-sh/setup-uv@v7
         with: