Bump djangorestframework from 3.15.1 to 3.15.2 in /requirements

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.15.1 to 3.15.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](https://github.com/encode/django-rest-framework/compare/3.15.1...3.15.2)

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

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

requirements/requirements.txt

@@ -30,4 +30,4 @@ django-localflavor==4.0
 django-material-admin==1.8.6
 django-tinymce==4.0.0
 django-weasyprint==2.3.0
-djangorestframework==3.15.1
+djangorestframework==3.15.2