[requirements-dev.txt]: Update isort

Update isort from `>=5.0, <6.0` to `>=6.0, <7.0`.

Author: andthum

requirements-dev.txt

@@ -17,7 +17,7 @@ flake8-isort >=6.0, <7.0
 flake8-logging-format >=0.1, <1.0
 flake8-pytest-style >=2.0, <3.0
 flake8-rst-docstrings >=0.2.6, <1.0
-isort >=5.0, <6.0
+isort >=6.0, <7.0
 pep8-naming >=0.1, <1.0
 pre-commit >=4.0, <5.0
 pytest >=8.0, <9.0