Bump djangorestframework from 3.13.1 to 3.15.2

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.13.1 to 3.15.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.13.1...3.15.2)

---
updated-dependencies:
- dependency-name: djangorestframework
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -25,7 +25,7 @@ django-crispy-forms==1.10.0
 django-environ==0.8.1
 django-filter==21.1
 django-widget-tweaks==1.4.12
-djangorestframework==3.13.1
+djangorestframework==3.15.2
 doc8==0.11.1
 docker==5.0.3
 dockerpty==0.4.1