Bump flake8 from 4.0.1 to 6.0.0

Bumps [flake8](https://github.com/pycqa/flake8) from 4.0.1 to 6.0.0.
- [Release notes](https://github.com/pycqa/flake8/releases)
- [Commits](PyCQA/flake8@4.0.1...6.0.0)

---
updated-dependencies:
- dependency-name: flake8
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements_dev.txt

@@ -4,7 +4,7 @@
 #---------------------------------------------------------
 backports.cached-property==1.0.2; python_version<="3.7"
 coveralls==3.3.1
-flake8==5.0.4
+flake8==6.0.0
 pillow==9.3.0
 pytest==7.2.0
 pytest-cache==1.0