build: bump django from 3.2.14 to 3.2.15 in /docs (#7379)

Bumps [django](https://github.com/django/django) from 3.2.14 to 3.2.15.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@3.2.14...3.2.15)

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

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Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/requirements.txt

@@ -26,7 +26,7 @@ coverage==6.3.2
     # via -r requirements.in
 datetime==4.4
     # via -r requirements.in
-django==3.2.14
+django==3.2.15
     # via
     #   -r requirements.in
     #   django-classy-tags