Fix warnings_checker.dart handling of multitests

tests/language/sync_generator1_test.dart

Index: tests/language/sync_generator1_test.dart
diff --git a/tests/language/sync_generator1_test.dart b/tests/language/sync_generator1_test.dart
index 88e1fd409c1b4b5db9440b7da239aea87e68c6d9..565c5038a6c62542ca32fee6e62be9583874c79c 100644
--- a/tests/language/sync_generator1_test.dart
+++ b/tests/language/sync_generator1_test.dart
@@ -44,7 +44,7 @@ einsZwei() sync* {
 
 dreiVier() sync* {
   // Throws type error: yielded object is not an iterable.
-  yield* 3; /// 01: static type warning
+  yield* 3; //# 01: static type warning
 }
 
 main() {
@@ -80,6 +80,6 @@ main() {
     print(einsZwei());
     Expect.equals("(1, 2, 3, 5, [6])", einsZwei().toString());
 
-    Expect.throws(() => dreiVier().toString()); /// 01: continued
+    Expect.throws(() => dreiVier().toString()); //# 01: continued
   }
 }