ci: Bump the lint Python version to 3.7

Author: achimnol

.github/workflows/lint-flake8.yml

@@ -9,10 +9,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v1
-    - name: Set up Python 3.6
+    - name: Set up Python 3.7
       uses: actions/setup-python@v1
       with:
-        python-version: 3.6
+        python-version: 3.7
     - name: Install dependencies
       run: |
         python -m pip install -U pip setuptools