switch CI to uv

.gitea/workflows/tests.yaml

@@ -19,14 +19,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+      - name: Install uv
+        uses: astral-sh/setup-uv@v6
       - name: Set up Python
-        uses: actions/setup-python@v5
+        run: uv python install
-        with:
-          python-version: '3.12'
-          cache: 'pip'
-      - run: pip install -r requirements.txt
       - name: Install the code linting and formatting tool Ruff
-        run: pip install ruff
+        run: uv build
       - name: Lint code with Ruff
         run: ruff check --output-format=github --target-version=py39
       - name: Check code formatting with Ruff