[CI] dont source venv in a subshell

let's see how that goes

.woodpecker/workflow.yaml

@@ -16,7 +16,7 @@ steps:
       ENV_PATH: .env.ci
     commands:
       - python -m venv venv
-      - /bin/bash -c "source venv/bin/activate"
+      - source venv/bin/activate
       - echo VENV is $VIRTUAL_ENV
       - python -m pip install --root-user-action=ignore --disable-pip-version-check --no-input --quiet -r requirements/test.txt
       - python -m pytest