Update flake8 to 4.0.1 in requirements-linting.txt to fix failing linting build

[gaugup]

Description

It seems the linting build is failing with the following error:-

Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.7.14/x64/bin/flake[8](https://github.com/microsoft/responsible-ai-toolbox/actions/runs/3175056318/jobs/5172629653#step:5:9)", line 8, in <module>
    sys.exit(main())
  File "/opt/hostedtoolcache/Python/3.7.[14](https://github.com/microsoft/responsible-ai-toolbox/actions/runs/3175056318/jobs/5172629653#step:5:15)/x64/lib/python3.7/site-packages/flake8/main/cli.py", line 22, in main
    app.run(argv)
  File "/opt/hostedtoolcache/Python/3.7.14/x64/lib/python3.7/site-packages/flake8/main/application.py", line 363, in run
    self._run(argv)
  File "/opt/hostedtoolcache/Python/3.7.14/x64/lib/python3.7/site-packages/flake8/main/application.py", line 350, in _run
    self.initialize(argv)
  File "/opt/hostedtoolcache/Python/3.7.14/x64/lib/python3.7/site-packages/flake8/main/application.py", line 330, in initialize
    self.find_plugins(config_finder)
  File "/opt/hostedtoolcache/Python/3.7.14/x64/lib/python3.7/site-packages/flake8/main/application.py", line [15](https://github.com/microsoft/responsible-ai-toolbox/actions/runs/3175056318/jobs/5172629653#step:5:16)3, in find_plugins
    self.check_plugins = plugin_manager.Checkers(local_plugins.extension)
  File "/opt/hostedtoolcache/Python/3.7.14/x64/lib/python3.7/site-packages/flake8/plugins/manager.py", line 357, in __init__
    self.namespace, local_plugins=local_plugins
  File "/opt/hostedtoolcache/Python/3.7.14/x64/lib/python3.7/site-packages/flake8/plugins/manager.py", line [23](https://github.com/microsoft/responsible-ai-toolbox/actions/runs/3175056318/jobs/5172629653#step:5:24)8, in __init__
    self._load_entrypoint_plugins()
  File "/opt/hostedtoolcache/Python/3.7.14/x64/lib/python3.7/site-packages/flake8/plugins/manager.py", line [25](https://github.com/microsoft/responsible-ai-toolbox/actions/runs/3175056318/jobs/5172629653#step:5:26)4, in _load_entrypoint_plugins
    eps = importlib_metadata.entry_points().get(self.namespace, ())
AttributeError: 'EntryPoints' object has no attribute 'get'
Error: Process completed with exit code 1.

Pinning flake8 to 4.0.1 fixes this error.

Checklist

• I have added screenshots above for all UI changes.
• I have added e2e tests for all UI changes.
• Documentation was updated if it was needed.

[github-actions]

https://responsibleai.blob.core.windows.net/pullrequest/microsoft/responsible-ai-toolbox/gaugup/FixLintingBuild/dashboard/index.html

[codecov-commenter]

Codecov Report

Merging #1760 (1fbb0eb) into main (f3fad40) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1760   +/-   ##
=======================================
  Coverage   88.30%   88.30%           
=======================================
  Files          89       89           
  Lines        5250     5250           
=======================================
  Hits         4636     4636           
  Misses        614      614           

Flag	Coverage Δ
unittests	88.30% <ø> (ø)

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