Add flake8

Author: Ric Janus Sapasap

.github/workflows/tests.yml

@@ -16,4 +16,7 @@ jobs:
         run: sudo apt-get update && sudo apt-get install -y xmlsec1
       - name: Install tox
         run: pip install tox
-      - run: tox
+      - name: Install flake8
+        run: pip install flake8
+      - run: tox
+      - run: flake8