Fixed #34634 -- Adjusted system check for clashing fields to warn about links to common parent for MTI models.

tests/invalid_models_tests/test_models.py

@@ -1070,6 +1070,31 @@ class ShadowingFieldsTests(SimpleTestCase):
             ],
         )
 
+    def test_diamond_mti_common_parent(self):
+        class GrandParent(models.Model):
+            pass
+
+        class Parent(GrandParent):
+            pass
+
+        class Child(Parent):
+            pass
+
+        class MTICommonParentModel(Child, GrandParent):
+            pass
+
+        self.assertEqual(
+            MTICommonParentModel.check(),
+            [
+                Error(
+                    "The field 'grandparent_ptr' clashes with the field "
+                    "'grandparent_ptr' from model 'invalid_models_tests.parent'.",
+                    obj=MTICommonParentModel,
+                    id="models.E006",
+                )
+            ],
+        )
+
     def test_id_clash(self):
         class Target(models.Model):
             pass