Describe the bug
index_together has been deprecated in newer versions of Django, and the package has not yet been updated to reflect this change.

To Reproduce
Steps to reproduce the behavior:

1. Install the package using pip install django-notifications-hq
2. add the Django Notifications to your project
3. Start Django server

Expected behavior
Modify the Package to this

from django.db.models import Index

class Meta:
    indexes = [
        Index(fields=['actor_content_type', 'actor_object_id']),
    ]