Refs #29444 -- Allowed returning multiple fields from INSERT statements on PostgreSQL.

Thanks Florian Apolloner, Tim Graham, Simon Charette, Nick Pope, and
Mariusz Felisiak for reviews.

tests/queries/models.py

@@ -4,6 +4,7 @@ Various complex queries that have been problematic in the past.
 import threading
 
 from django.db import models
+from django.db.models.functions import Now
 
 
 class DumbCategory(models.Model):
@@ -730,3 +731,19 @@ class RelatedIndividual(models.Model):
 class CustomDbColumn(models.Model):
     custom_column = models.IntegerField(db_column='custom_name', null=True)
     ip_address = models.GenericIPAddressField(null=True)
+
+
+class CreatedField(models.DateTimeField):
+    db_returning = True
+
+    def __init__(self, *args, **kwargs):
+        kwargs.setdefault('default', Now)
+        super().__init__(*args, **kwargs)
+
+
+class ReturningModel(models.Model):
+    created = CreatedField(editable=False)
+
+
+class NonIntegerPKReturningModel(models.Model):
+    created = CreatedField(editable=False, primary_key=True)