Bump isort from 5.5.4 to 5.6.4

Bumps [isort](https://github.com/pycqa/isort) from 5.5.4 to 5.6.4.
- [Release notes](https://github.com/pycqa/isort/releases)
- [Changelog](https://github.com/PyCQA/isort/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/pycqa/isort/compare/5.5.4...5.6.4)

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

requirements.txt

 flake8==3.8.3
 flake8-debugger==3.2.1
 flake8-blind-except==0.1.1
-isort==5.5.4
+isort==5.6.4
 
 # Helpers
 pyprof2calltree==1.4.5