[Security] Bump django from 3.1 to 3.1.6
[Security] Bump django from 3.1 to 3.1.6

Bumps [django](https://github.com/django/django) from 3.1 to 3.1.6. **This update includes security fixes.**
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/3.1...3.1.6)

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