fix: order of model classes in the unique_constraint_by_fields

Author: s-aleshin

rest_framework/serializers.py

@@ -1608,7 +1608,7 @@ def get_unique_together_validators(self):
 
         unique_constraint_by_fields = {
             constraint.fields: constraint
-            for model_cls in (self.Meta.model, *self.Meta.model._meta.parents)
+            for model_cls in (*self.Meta.model._meta.parents, self.Meta.model)
             for constraint in model_cls._meta.constraints
             if isinstance(constraint, models.UniqueConstraint)
         }