Fixes #2059. Don't expect an error in a weak mode (#2060)

Author: sgrekhov

LanguageFeatures/nnbd/weak/const_evaluation_A06_t01.dart

@@ -11,19 +11,15 @@
 
 // Requirements=nnbd-weak
 
+import "../../../Utils/expect.dart";
 import '../const_evaluation_lib.dart';
 import 'const_evaluation_legacy_lib.dart';
 
 const dynamic d = null;
 
 main() {
   const c1 = C.t(null, cLegacyInt);
-//           ^^^^^^^^^^^^^^^^^^^^^
-// [analyzer] unspecified
-// [cfe] unspecified
-
   const c2 = C.t(d, cLegacyInt);
-//           ^^^^^^^^^^^^^^^^^^
-// [analyzer] unspecified
-// [cfe] unspecified
+  Expect.isNull(c1.x);
+  Expect.isNull(c2.x);
 }