Bump django from 3.1.4 to 3.1.12 (#67)

Bumps [django](https://github.com/django/django) from 3.1.4 to 3.1.12.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/3.1.4...3.1.12

)

---
updated-dependencies:
- dependency-name: django
  dependency-type: direct:development
...

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dev-requirements.txt

 -r dev-env-requirements.txt
-django==3.1.4
+django==3.1.12