Update isort requirement from <5.6,>=5.1 to >=5.1,<5.7
Update isort requirement from <5.6,>=5.1 to >=5.1,<5.7

Updates the requirements on [isort](https://github.com/pycqa/isort) to permit the latest version.
- [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/5.1.0...5.6.4)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
django-oscar/django-oscar-stores,django-oscar/django-oscar-stores,django-oscar/django-oscar-stores