Fix django deprecation warnings (#4712)

tests/test_model_serializer.py

@@ -94,7 +94,7 @@ class Issue3674ParentModel(models.Model):
 
 
 class Issue3674ChildModel(models.Model):
-    parent = models.ForeignKey(Issue3674ParentModel, related_name='children')
+    parent = models.ForeignKey(Issue3674ParentModel, related_name='children', on_delete=models.CASCADE)
     value = models.CharField(primary_key=True, max_length=64)
 
 
@@ -1013,7 +1013,7 @@ class Issue3674Test(TestCase):
             title = models.CharField(max_length=64)
 
         class TestChildModel(models.Model):
-            parent = models.ForeignKey(TestParentModel, related_name='children')
+            parent = models.ForeignKey(TestParentModel, related_name='children', on_delete=models.CASCADE)
             value = models.CharField(primary_key=True, max_length=64)
 
         class TestChildModelSerializer(serializers.ModelSerializer):

tests/test_prefetch_related.py

@@ -2,6 +2,7 @@ from django.contrib.auth.models import Group, User
 from django.test import TestCase
 
 from rest_framework import generics, serializers
+from rest_framework.compat import set_many
 from rest_framework.test import APIRequestFactory
 
 factory = APIRequestFactory()
@@ -22,7 +23,7 @@ class TestPrefetchRelatedUpdates(TestCase):
     def setUp(self):
         self.user = User.objects.create(username='tom', email='tom@example.com')
         self.groups = [Group.objects.create(name='a'), Group.objects.create(name='b')]
-        self.user.groups = self.groups
+        set_many(self.user, 'groups', self.groups)
         self.user.save()
 
     def test_prefetch_related_updates(self):