flake8 7 pin rather

setup.py

@@ -80,7 +80,7 @@
     # Test dependencies (unit tests)
     # Execute `pip install .[test]` once and then use `pytest` to run tests
     'test': [
-        'flake8<6',  # code style not updated to major release 6
+        'flake8<7',  # code style not updated to major release 7
         'pytest>=3.9,!=6.0.0rc1,!=6.0.0',
         'pytest-cov>=2.10.1',
         'pytest-env',