fix CI: pin Python 3.13.11 to match container image

Use uv python pin + only-system preference to prevent uv from
downloading a different Python version and wiping the venv.

.woodpecker/ci.yml

@@ -8,16 +8,24 @@ when:
 steps:
   - name: lint
     image: ghcr.io/astral-sh/uv:python3.13-bookworm-slim
+    environment:
+      UV_PYTHON_PREFERENCE: only-system
+      UV_LINK_MODE: copy
     commands:
-      - uv sync --dev --python 3.13
+      - uv python pin 3.13.11
+      - uv sync --dev
       - uv pip install -e .
       - uv run ruff check src/ tests/ --output-format=concise
       - uv run ruff format --check src/ tests/
 
   - name: test
     image: ghcr.io/astral-sh/uv:python3.13-bookworm-slim
+    environment:
+      UV_PYTHON_PREFERENCE: only-system
+      UV_LINK_MODE: copy
     commands:
-      - uv sync --dev --python 3.13
+      - uv python pin 3.13.11
+      - uv sync --dev
       - uv pip install -e .
       - uv run pytest tests/ --no-cov --tb=short -q