[ci] perhaps /bin/sh prefers . over source

.woodpecker/workflow.yaml

@@ -26,7 +26,7 @@ steps:
     image: docker.io/astral/uv:python${PYTHON_VERSION}-trixie-slim
     commands:
       - python -m venv venv
-      - source venv/bin/activate
+      - . venv/bin/activate
       - python -m pip install -r requirements.txt -r requirements.dev.txt
       - python -m pytest tests.py
       # coverage: uv run pytest tests.py --cov-report= --cov=src # no cov report on terminal: useful for CI