Add python setup hook.

.github/workflows/development.yaml

@@ -25,6 +25,10 @@ jobs:
             mysql_ver: "5.7"
     steps:
       - uses: actions/checkout@v2
+      - name: Set up Python ${{matrix.py_ver}}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{matrix.py_ver}}
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip