Bump isort from 5.8.0 to 5.9.1

Bumps [isort](https://github.com/pycqa/isort) from 5.8.0 to 5.9.1.
- [Release notes](https://github.com/pycqa/isort/releases)
- [Changelog](https://github.com/PyCQA/isort/blob/main/CHANGELOG.md)
- [Commits](https://github.com/pycqa/isort/compare/5.8.0...5.9.1)

---
updated-dependencies:
- dependency-name: isort
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

requirements-dev.txt

@@ -13,7 +13,7 @@ pytest-asyncio==0.15.1
 pytest-cov==2.12.1
 pytest-mock==3.6.1
 pytest-random-order==1.0.4
-isort==5.8.0
+isort==5.9.1
 
 # Convert jupyter notebooks to markdown documents
 nbconvert==6.0.7