Update flake8-isort requirement in /requirements

Updates the requirements on [flake8-isort](https://github.com/gforcada/flake8-isort) to permit the latest version.
- [Changelog](https://github.com/gforcada/flake8-isort/blob/main/CHANGES.rst)
- [Commits](gforcada/flake8-isort@4.1.0...6.1.1)

---
updated-dependencies:
- dependency-name: flake8-isort
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements/development.txt

@@ -4,7 +4,7 @@
 black
 
 flake8-builtins>=1.5,<2.3
-flake8-isort>=4.1,<4.3
+flake8-isort>=4.1,<6.2
 flake8-qgis>=1,<1.1
 pylint>=2,<3
 isort>=5.8,<5.14