Bump isort from 5.8.0 to 5.9.1 (#82)

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](PyCQA/isort@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>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements-dev.txt

@@ -1,4 +1,4 @@
-isort==5.8.0
+isort==5.9.1
 black==21.6b0
 sphinx==4.0.2
 pytest==6.2.4