Fixed #32812 -- Restored immutability of named values from QuerySet.values_list().

Regression in 981a072dd4.

Thanks pirelle for the report.

tests/model_utils/tests.py

@@ -0,0 +1,10 @@
+from django.db.models.utils import create_namedtuple_class
+from django.test import SimpleTestCase
+
+
+class NamedTupleClassTests(SimpleTestCase):
+    def test_immutability(self):
+        row_class = create_namedtuple_class('field1', 'field2')
+        row = row_class('value1', 'value2')
+        with self.assertRaises(AttributeError):
+            row.field3 = 'value3'