Bump django from 4.2.18 to 4.2.20 in /docs/_ext/djangodummy

Bumps [django](https://github.com/django/django) from 4.2.18 to 4.2.20.
- [Commits](django/django@4.2.18...4.2.20)

---
updated-dependencies:
- dependency-name: django
  dependency-version: 4.2.20
  dependency-type: direct:production
...

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

Author: dependabot[bot]

docs/_ext/djangodummy/requirements.txt

@@ -1,6 +1,6 @@
 # for readthedocs
 # Remaining requirements are picked up from setup.py
-Django == 4.2.18
+Django == 4.2.20
 django-extra-views == 0.14.0
 sphinxcontrib-django == 0.5.1
 sphinx_rtd_theme==2.0.0