Bump djangorestframework from 3.12.4 to 3.15.2 in /server

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.12.4 to 3.15.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.12.4...3.15.2)

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

Signed-off-by: dependabot[bot] <[email protected]>

server/requirements.txt

@@ -5,7 +5,7 @@ coreapi==2.3.3
 coreschema==0.0.4
 dj-database-url==0.5.0
 Django==3.2.25
-djangorestframework==3.12.4
+djangorestframework==3.15.2
 django-extensions==3.1.5
 django-heroku==0.3.1
 django-redis==5.2.0