Log Message:
py-django-mptt: updated to 0.15.0

0.15

Since I unfortunately still depend on django-mptt in prehistoric projects I took \ 
it upon me to make it runnable again. This doesn't mean I want to maintain the \ 
package.
Added Django 4.2.
Dropped Python < 3.9, Django < 3.2.
Started using ruff and more rules.
Dropped the index_together check on Django 5 and better. Django 5 only supports \ 
Meta.indexes.
Optimized tree rebuilding.
Added support for the Django admin theme switcher.
Switched to hatchling.