Ensure venv cache is healthy

Author: sdispater

.github/workflows/tests.yml

@@ -55,10 +55,16 @@ jobs:
 
       - name: Set up cache
         uses: actions/cache@v2
+        id: cache
         with:
           path: .venv
           key: venv-${{ runner.os }}-${{ steps.full-python-version.outputs.version }}-${{ hashFiles('**/poetry.lock') }}
-    
+
+      - name: Ensure cache is healthy
+        if: steps.cache.outputs.cache-hit == 'true'
+        shell: bash
+        run: timeout 10s poetry run pip --version || rm -rf .venv
+
       - name: Install dependencies
         shell: bash
         run: |