Remove `flake8` upper constraint

[pawelad]

Hi!

Is there any reason for the flake8 upper constraint?

https://github.com/rocioar/flake8-django/blob/808284f7e0227c6e7ad9f6d4721c6b79c1b863be/pyproject.toml#L27

Version 6 of flake8 was recently released (https://flake8.pycqa.org/en/latest/release-notes/6.0.0.html) but I can't upgrade because of this upper constraint.

Here are some helpful articles that (among other things) lay out why packages shouldn't provide upper version constraints of it's dependencies:

• https://hynek.me/articles/semver-will-not-save-you/
• https://iscinumpy.dev/post/bound-version-constraints/
• https://bernat.tech/posts/version-numbers/

[pawelad]

Related to #103, but I'd still vote to remove the <7 constraint from there.

[pietzschke]

+1 same situation with the new v7 version