[6.0.x] Fixed #36611, Refs #36580 -- Added system check for multicolumn ForeignObject in Meta.indexes/constraints/unique_together.

ForeignObjects with multiple `from_fields` are not supported in these
options.

Co-authored-by: Jacob Walls <jacobtylerwalls@gmail.com>
Co-authored-by: Natalia <124304+nessita@users.noreply.github.com>

Backport of 5b51e6f759 from main.

tests/invalid_models_tests/test_models.py

@@ -166,6 +166,54 @@ class UniqueTogetherTests(SimpleTestCase):
             ],
         )
 
+    def test_pointing_to_foreign_object(self):
+        class Reference(models.Model):
+            reference_id = models.IntegerField(unique=True)
+
+        class ReferenceTab(models.Model):
+            reference_id = models.IntegerField()
+            reference = models.ForeignObject(
+                Reference,
+                from_fields=["reference_id"],
+                to_fields=["reference_id"],
+                on_delete=models.CASCADE,
+            )
+
+            class Meta:
+                unique_together = [["reference"]]
+
+        self.assertEqual(ReferenceTab.check(), [])
+
+    def test_pointing_to_foreign_object_multi_column(self):
+        class Reference(models.Model):
+            reference_id = models.IntegerField(unique=True)
+            code = models.CharField(max_length=1)
+
+        class ReferenceTabMultiple(models.Model):
+            reference_id = models.IntegerField()
+            code = models.CharField(max_length=1)
+            reference = models.ForeignObject(
+                Reference,
+                from_fields=["reference_id", "code"],
+                to_fields=["reference_id", "code"],
+                on_delete=models.CASCADE,
+            )
+
+            class Meta:
+                unique_together = [["reference"]]
+
+        self.assertEqual(
+            ReferenceTabMultiple.check(),
+            [
+                Error(
+                    "'unique_together' refers to a ForeignObject 'reference' with "
+                    "multiple 'from_fields', which is not supported for that option.",
+                    obj=ReferenceTabMultiple,
+                    id="models.E049",
+                ),
+            ],
+        )
+
 
 @isolate_apps("invalid_models_tests")
 class IndexesTests(TestCase):