Bump django-modelcluster from 6.0 to 6.3 (#4342)

Bumps [django-modelcluster](https://github.com/wagtail/django-modelcluster) from 6.0 to 6.3.
- [Release notes](https://github.com/wagtail/django-modelcluster/releases)
- [Changelog](https://github.com/wagtail/django-modelcluster/blob/main/CHANGELOG.txt)
- [Commits](wagtail/django-modelcluster@v6.0...v6.3)

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

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

requirements.txt

@@ -151,7 +151,7 @@ django-large-image==0.8.1
     # via geotrek (setup.py)
 django-leaflet==0.19.post11
     # via mapentity
-django-modelcluster==6.0
+django-modelcluster==6.3
     # via geotrek (setup.py)
 django-modeltranslation==0.18.11
     # via mapentity