isort limits python_require <4.0 (again)

[sisp]

In #1877 the issue of having a cap on the Python version was raised. #1878 fixed this problem and was merged. 🎉

@timothycrosley Any specific reason why you re-introduced the cap in 9e4b5ee again? It breaks any downstream project that uses Poetry with an uncapped Python version. 😞

[staticdev]

@sisp @yajo fixed on 5.11.0.

[sisp]

Thanks, @staticdev! 🙏