Flake8: Only enable default tests

setup.cfg

@@ -14,7 +14,8 @@ known_standard_library = _dummy_thread,_thread,abc,aifc,argparse,array,ast,async
 known_third_party = defusedxml,passlib,pkg_resources,pytest,vobject
 
 [flake8]
-extend-ignore = H
+# Only enable default tests (https://github.com/PyCQA/flake8/issues/790#issuecomment-812823398)
+select = E,F,W,C90,DOES-NOT-EXIST
 
 [mypy]
 ignore_missing_imports = True