Update test as combined member signature would fail

Change-Id: Ifc336b706fa1315f206f2214eb233489bd21c763
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/96645
Reviewed-by: Erik Ernst <eernst@google.com>
Reviewed-by: Aske Simon Christensen <askesc@google.com>
diff --git a/tests/language_2/cascaded_forwarding_stubs_test.dart b/tests/language_2/cascaded_forwarding_stubs_test.dart
index 1af182b..a10cc2e 100644
--- a/tests/language_2/cascaded_forwarding_stubs_test.dart
+++ b/tests/language_2/cascaded_forwarding_stubs_test.dart
@@ -24,7 +24,9 @@
 }
 
 // E contains a forwarding stub for f which ensures that `y` is type checked.
-class E extends D implements I2 {}
+class E extends D implements I2 {
+  void f(B x, B y);
+}
 
 main() {
   E e = new E();