Bump django in /backend in the pip group across 1 directory

Bumps the pip group with 1 update in the /backend directory: [django](https://github.com/django/django).


Updates `django` from 5.1.4 to 5.1.13
- [Commits](django/django@5.1.4...5.1.13)

---
updated-dependencies:
- dependency-name: django
  dependency-version: 5.1.13
  dependency-type: direct:production
  dependency-group: pip
...

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

Author: dependabot[bot]

backend/pyproject.toml

@@ -44,7 +44,7 @@ known-first-party = [
 [project]
 requires-python = ">=3.13.5"
 dependencies = [
-    "django==5.1.4",
+    "django==5.1.13",
     "django-environ==0.10.0",
     "django-model-utils==5.0.0",
     "django-timezone-field==7.0",