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@4.0.0...6.1.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements/development.txt

@@ -6,6 +6,6 @@
 black
 flake8>=3.8,<5.1
 flake8-builtins>=1.5,<2.1
-flake8-isort>=4.0,<4.3
+flake8-isort>=4.0,<6.2
 isort>=5.7,<5.11
 pre-commit>=2.12,<2.21