isort limits python_require to <4.0

[staticdev]

It is not possible for instance to create a project that uses isort and require python>=3.9 for instance. Solver will have a message like:

Because no versions of isort match >5.10.1,<6.0.0
   and isort (5.10.1) requires Python >=3.6.1,<4.0, isort is forbidden.
  So, because your-package depends on isort (^5.10.1), version solving failed.

It would be nice to soften this requirement, since there is no real information that shows isort will stop working on python 4.0.

There is an extensive article with ideas of why one should not limit that: https://iscinumpy.dev/post/bound-version-constraints/