pylint: use python 3.9 and setup-python@2

ci/pylint.yml

@@ -9,10 +9,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.8
-      uses: actions/setup-python@v1
+    - name: Set up Python 3.9
+      uses: actions/setup-python@v2
       with:
-        python-version: 3.8
+        python-version: 3.9
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip