Update test.yml

.github/workflows/test.yml

@@ -36,6 +36,11 @@ jobs:
       - name: Check out repository code
         uses: actions/checkout@v2
 
+      - name: Set up Python 3.8
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.8'
+
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip