chore(deps): bump django from 4.2.15 to 4.2.20 in /backend

Bumps [django](https://github.com/django/django) from 4.2.15 to 4.2.20.
- [Commits](django/django@4.2.15...4.2.20)

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

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

Author: dependabot[bot]

backend/requirements.txt

@@ -16,7 +16,7 @@ crontab==1.0.1
 cryptography==42.0.4
 defusedxml==0.7.1
 dj-rest-auth==7.0.1
-Django==4.2.16
+Django==4.2.20
 django-allauth==65.4.1
 django-cors-headers==3.14.0
 django-filter==23.1