Flake8 pre-commit dependency has moved

[ruben-chainalysis]

Flake8 has moved to GitHub and this breaks the pre-commit hook using the now 404 Gitlab URL.

Running tox -e lint locally gives an error like the following:

[INFO] Initializing environment for https://gitlab.com/pycqa/flake8.
An unexpected error has occurred: CalledProcessError: command: ('/thisiswhereyourbinis/bin/git', 'fetch', 'origin', '--tags')
return code: 128
expected return code: 0
stdout: (none)
stderr:
    remote: The project you were looking for could not be found or you don't have permission to view it.
    fatal: repository 'https://gitlab.com/pycqa/flake8.git/' not found

Check the log at /yourcacheplace/pre-commit/pre-commit.log
ERROR: InvocationError for command /yourProjectPath/PyGithub/.tox/lint/bin/pre-commit run --all-files --show-diff-on-failure (exited with code 3)
_________________________________________________________________________________________________________________________________________________________________________________ summary __________________________________________________________________________________________________________________________________________________________________________________
ERROR:   lint: commands failed

CI pipelines are breaking too with the following error:

[INFO] Initializing environment for https://gitlab.com/pycqa/flake8.
  An unexpected error has occurred: CalledProcessError: command: ('/usr/bin/git', 'fetch', 'origin', '--tags')
  return code: 128
  expected return code: 0
  stdout: (none)
  stderr:
      fatal: could not read Username for 'https://gitlab.com/': No such device or address
      
  Check the log at /home/runner/.cache/pre-commit/pre-commit.log
  Error: ERROR: InvocationError for command /home/runner/work/PyGithub/PyGithub/.tox/lint/bin/pre-commit run --all-files --show-diff-on-failure (exited with code 3)
py38 create: /home/runner/work/PyGithub/PyGithub/.tox/py38

It's a quick fix, easier than creating this issue, but I'm creating it because it's the first place I look for problems and others might benefit from it. Will submit PR in a minute.

[cclauss]

This can be closed as fixed in #2380