Bump django from 3.2.9 to 3.2.18 in /docs/_ext/djangodummy

Bumps [django](https://github.com/django/django) from 3.2.9 to 3.2.18.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@3.2.9...3.2.18)

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

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

Author: dependabot[bot]

docs/_ext/djangodummy/requirements.txt

@@ -1,5 +1,5 @@
 # for readthedocs
 # Remaining requirements are picked up from setup.py
-Django == 3.2.9
+Django == 3.2.18
 django-extra-views == 0.14.0
 sphinxcontrib-django == 0.5.1