Fix warnings_checker.dart handling of multitests

tests/language/string_interpolation6_test.dart

Index: tests/language/string_interpolation6_test.dart
diff --git a/tests/language/string_interpolation6_test.dart b/tests/language/string_interpolation6_test.dart
index 155f9fbc09f35b9cd88e51adff39ff38429aa740..35a5b85195c6473dbb1fd30ee7678af8ad5328ec 100644
--- a/tests/language/string_interpolation6_test.dart
+++ b/tests/language/string_interpolation6_test.dart
@@ -8,7 +8,7 @@ class StringInterpolation6NegativeTest {
   static testMain() {
     // Dollar not followed by "{" or identifier.
     String regexp;
-    regexp = "^(\\d\\d?)[-/](\\d\\d?)$"; /// 01: compile-time error
+    regexp = "^(\\d\\d?)[-/](\\d\\d?)$"; //# 01: compile-time error
     print(regexp);
   }
 }