revert workflow change

.github/workflows/test.yml

@@ -27,7 +27,15 @@ jobs:
           version: 1.7.1
           virtualenvs-create: true
           virtualenvs-in-project: true
+      - name: cache deps
+        id: cache-deps
+        uses: actions/cache@v2
+        with:
+          path: .venv
+          key: pydeps-${{ hashFiles('**/poetry.lock') }}
       - run: poetry install --no-interaction --no-root
+        if: steps.cache-deps.outputs.cache-hit != 'true'
+      - run: poetry install --no-interaction
       - name: run unit tests with coverage
         id: fast-tests
         run: poetry run pytest --cov -m 'not slow'