chore(deps): bump django from 4.2.16 to 5.1.5 in /backend

Bumps [django](https://github.com/django/django) from 4.2.16 to 5.1.5.
- [Commits](django/django@4.2.16...5.1.5)

---
updated-dependencies:
- dependency-name: django
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

backend/requirements.txt

@@ -2,7 +2,7 @@ asgiref==3.8.1
 autopep8==2.3.1
 certifi==2024.8.30
 charset-normalizer==3.3.2
-Django==4.2.16
+Django==5.1.5
 django-cors-headers==4.6.0
 django-rest-passwordreset==1.4.2
 djangorestframework==3.15.2