Use more liberal flake8 for tests

Ignore rule W402 (wrong import order) to enable use of
pytest.importorskip.

.gitlab-ci.yml

@@ -481,7 +481,9 @@ flake8:
       artifacts: true
   script:
     - *configure
-    - flake8 --max-line-length=80 $(git ls-files '*.py' | grep -vE '(ans\.py|dangerfile\.py)')
+    - flake8 --max-line-length=80 $(git ls-files '*.py' | grep -vE '(ans\.py|dangerfile\.py|^bin/tests/system/)')
+      # Ignore Flake8 E402 error (module level import not at top of file) in system test to enable use of pytest.importorskip
+    - flake8 --max-line-length=80 --extend-ignore=E402 $(git ls-files 'bin/tests/system/*.py' | grep -vE 'ans\.py')
 
 pylint:
   <<: *default_triggering_rules