wagtail.contrib.modeladmin No longer available in Wagtail 6.0

[andrew-kyle92]

Wagtail announced that the ModelAdmin app will be removed in v6.0, but will still be available as an external package here, wagtail_modeladmin.

In wagtailgridder/wagtail_hooks.py, you're importing:
from wagtail.contrib.modeladmin.options import PageButtonHelper
This needs to be changed to:
from wagtail_modeladmin.options import PageButtonHelper
Once wagtail_modeladmin is installed.

Also, this needs to be changed as well:
from wagtail.contrib.modeladmin.options import ( ModelAdmin, ModelAdminGroup, modeladmin_register, )
To
from wagtail_modeladmin.options import ( ModelAdmin, ModelAdminGroup, modeladmin_register, )