Bump djangorestframework from 3.15.2 to 3.16.0

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.15.2 to 3.16.0.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.15.2...3.16.0)

---
updated-dependencies:
- dependency-name: djangorestframework
  dependency-version: 3.16.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]