Bump django-mptt from 0.16.0 to 0.18.0

Bumps [django-mptt](https://github.com/django-mptt/django-mptt) from 0.16.0 to 0.18.0.
- [Release notes](https://github.com/django-mptt/django-mptt/releases)
- [Changelog](https://github.com/django-mptt/django-mptt/blob/main/CHANGELOG.rst)
- [Commits](django-mptt/django-mptt@0.16...0.18)

---
updated-dependencies:
- dependency-name: django-mptt
  dependency-version: 0.18.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements/docs.txt

@@ -9,6 +9,6 @@ sphinx-notfound-page
 # for extracting model docs
 django==3.2.25
 djangorestframework==3.14.0
-django-mptt==0.16.0
+django-mptt==0.18.0
 rsa==3.4.2
 ifcfg==0.21