Add linter (flake8) to Github action biuld_and_test

Author: xispa

.github/workflows/build-and-test.yml

@@ -25,6 +25,10 @@ jobs:
           bin/pip install -r requirements.txt
           bin/buildout -N -t 3 annotate
           bin/buildout -N -t 3
+      - name: lint
+        run: |
+          bin/pip install flake8
+          bin/flake8 --config ci_flake8.cfg src/senaite/
       - name: test
         run: |
           bin/test -s senaite.ast.tests