Bump django from 5.1.1 to 5.1.15

Bumps [django](https://github.com/django/django) from 5.1.1 to 5.1.15.
- [Commits](django/django@5.1.1...5.1.15)

---
updated-dependencies:
- dependency-name: django
  dependency-version: 5.1.15
  dependency-type: direct:production
...

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

Author: dependabot[bot]

docs/rtd_requirements.txt

@@ -1,5 +1,5 @@
 coverage
-django>=2.2,<=4.2
+django>=2.2,<=5.1.15
 django-haystack>=2.8,<=3.2
 djangorestframework>=3.7.0,<=3.13
 elasticsearch>=2.0.0,<=8.3.3