Fix warnings_checker.dart handling of multitests

tests/language/method_override2_test.dart

Index: tests/language/method_override2_test.dart
diff --git a/tests/language/method_override2_test.dart b/tests/language/method_override2_test.dart
index 63eb4310dd8e5fbbb7b677e3f4a9ad32057fb81b..f697efe7b8c99126a3a3b91b05f86a8c43fa2437 100644
--- a/tests/language/method_override2_test.dart
+++ b/tests/language/method_override2_test.dart
@@ -11,7 +11,7 @@ abstract class I {
 abstract class J extends I { }
 
 abstract class K extends J {
-  m({c, d}); // /// 00: static type warning
+  m({c, d}); // //# 00: static type warning
 }
 
 class C implements I {
@@ -21,9 +21,9 @@ class C implements I {
 }
 
 class D
-    extends C // /// 01: static type warning
-    implements I // /// 02: static type warning
-    implements J // /// 03: static type warning
+    extends C // //# 01: static type warning
+    implements I // //# 02: static type warning
+    implements J // //# 03: static type warning
 {
   m({c, d}) {
     print("$c $d");