update test workflow to include dev dependencies

.github/workflows/tests.yaml

@@ -21,8 +21,8 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        python -m pip install flake8 pytest wheel
         pip install -r requirements.txt
+        pip install -r requirements_dev.txt
     - name: Test with pytest
       run: |
         pytest tests