Fix warnings_checker.dart handling of multitests

tests/language/compile_time_constant_c_test.dart

Index: tests/language/compile_time_constant_c_test.dart
diff --git a/tests/language/compile_time_constant_c_test.dart b/tests/language/compile_time_constant_c_test.dart
index 72bacfbeb5b126dda49a2791bdb37996f8a25856..1a84633c367c80f5bc8a7db1ff375dfce2c17b88 100644
--- a/tests/language/compile_time_constant_c_test.dart
+++ b/tests/language/compile_time_constant_c_test.dart
@@ -6,13 +6,13 @@ const m0 = const {
   499: 400 + 99
 };
 const m1 = const {
-  "foo" + "bar": 42 //           /// 01: ok
+  "foo" + "bar": 42 //           //# 01: ok
 };
 const m2 = const {
-  "foo" * 4: 42 //               /// 02: compile-time error
+  "foo" * 4: 42 //               //# 02: compile-time error
 };
 const m3 = const {
-  "foo".codeUnitAt(0): 42 //     /// 03: compile-time error
+  "foo".codeUnitAt(0): 42 //     //# 03: compile-time error
 };
 
 use(x) => x;