Fix on delete cascade entity order

Since [#20708](https://github.com/netbox-community/netbox/pull/20708)
relation with a on delete RESTRICT are not deleted in the proper order.
Then the error `violate not-null constraint` occurs and breaks the
delete cascade feature.

netbox/core/signals.py

@@ -3,7 +3,7 @@ from threading import local
 
 from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import ObjectDoesNotExist, ValidationError
-from django.db.models import CASCADE
+from django.db.models import CASCADE, RESTRICT
 from django.db.models.fields.reverse_related import ManyToManyRel, ManyToOneRel
 from django.db.models.signals import m2m_changed, post_migrate, post_save, pre_delete
 from django.dispatch import receiver, Signal
@@ -47,6 +47,7 @@ clear_events = Signal()
 # Object types
 #
 
+
 @receiver(post_migrate)
 def update_object_types(sender, **kwargs):
     """
@@ -133,7 +134,7 @@ def handle_changed_object(sender, instance, **kwargs):
         prev_change := ObjectChange.objects.filter(
             changed_object_type=ContentType.objects.get_for_model(instance),
             changed_object_id=instance.pk,
-            request_id=request.id
+            request_id=request.id,
         ).first()
     ):
         prev_change.postchange_data = objectchange.postchange_data
@@ -172,9 +173,7 @@ def handle_deleted_object(sender, instance, **kwargs):
     try:
         run_validators(instance, validators)
     except ValidationError as e:
-        raise AbortRequest(
-            _("Deletion is prevented by a protection rule: {message}").format(message=e)
-        )
+        raise AbortRequest(_("Deletion is prevented by a protection rule: {message}").format(message=e))
 
     # Get the current request, or bail if not set
     request = current_request.get()
@@ -221,7 +220,12 @@ def handle_deleted_object(sender, instance, **kwargs):
             obj.snapshot()  # Ensure the change record includes the "before" state
             if type(relation) is ManyToManyRel:
                 getattr(obj, related_field_name).remove(instance)
-            elif type(relation) is ManyToOneRel and relation.null and relation.on_delete is not CASCADE:
+            elif (
+                type(relation) is ManyToOneRel
+                and relation.null
+                and relation.on_delete is not CASCADE
+                and relation.on_delete is not RESTRICT
+            ):
                 setattr(obj, related_field_name, None)
                 obj.save()
 
@@ -256,6 +260,7 @@ def clear_events_queue(sender, **kwargs):
 # DataSource handlers
 #
 
+
 @receiver(post_save, sender=DataSource)
 def enqueue_sync_job(instance, created, **kwargs):
     """
@@ -267,9 +272,10 @@ def enqueue_sync_job(instance, created, **kwargs):
         SyncDataSourceJob.enqueue_once(instance, interval=instance.sync_interval)
     elif not created:
         # Delete any previously scheduled recurring jobs for this DataSource
-        for job in SyncDataSourceJob.get_jobs(instance).defer('data').filter(
-            interval__isnull=False,
-            status=JobStatusChoices.STATUS_SCHEDULED
+        for job in (
+            SyncDataSourceJob.get_jobs(instance)
+            .defer('data')
+            .filter(interval__isnull=False, status=JobStatusChoices.STATUS_SCHEDULED)
         ):
             # Call delete() per instance to ensure the associated background task is deleted as well
             job.delete()