Bump djangorestframework from 3.14.0 to 3.15.2 in /requirements

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.14.0 to 3.15.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.14.0...3.15.2)

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

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

requirements/docs.txt

@@ -8,7 +8,7 @@ sphinx-notfound-page
 
 # for extracting model docs
 django==3.2.25
-djangorestframework==3.14.0
+djangorestframework==3.15.2
 django-mptt==0.16.0
 rsa==3.4.2
 ifcfg==0.21