Update CFE expectation for read_error_test.dart

Change-Id: Idfa1f83929305fbbc3560a1123850a1c785d6537
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/164880
Reviewed-by: Leaf Petersen <leafp@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
diff --git a/tests/language/nnbd/definite_assignment/read_error_test.dart b/tests/language/nnbd/definite_assignment/read_error_test.dart
index 2f08ad1..0894e58 100644
--- a/tests/language/nnbd/definite_assignment/read_error_test.dart
+++ b/tests/language/nnbd/definite_assignment/read_error_test.dart
@@ -1066,8 +1066,10 @@
     final dynamic x;
     x = 3;
     3 ?? x;
-    //   ^
-    // [analyzer] STATIC_WARNING.DEAD_NULL_AWARE_EXPRESSION
+//  ^
+// [cfe] Operand of null-aware operation '??' has type 'int' which excludes null.
+//       ^
+// [analyzer] STATIC_WARNING.DEAD_NULL_AWARE_EXPRESSION
   }
 }