Fix warnings_checker.dart handling of multitests

tests/corelib_strong/string_from_environment3_test.dart

Index: tests/corelib_strong/string_from_environment3_test.dart
diff --git a/tests/corelib_strong/string_from_environment3_test.dart b/tests/corelib_strong/string_from_environment3_test.dart
index 21af283b8ef24ce444b0ad25a5b82308b443b2de..962f5f1de0507713e1218d2b5e531bc9cf06d3e1 100644
--- a/tests/corelib_strong/string_from_environment3_test.dart
+++ b/tests/corelib_strong/string_from_environment3_test.dart
@@ -3,9 +3,9 @@
 // BSD-style license that can be found in the LICENSE file.
 
 main() {
-  const String.fromEnvironment('NOT_FOUND', defaultValue: 1); // /// 01: compile-time error
-  const String.fromEnvironment('NOT_FOUND', defaultValue: true); // /// 02: compile-time error
-  const String.fromEnvironment(null); // /// 03: compile-time error
-  const String.fromEnvironment(1); // /// 04: compile-time error
-  const String.fromEnvironment([]); // /// 05: compile-time error
+  const String.fromEnvironment('NOT_FOUND', defaultValue: 1); // //# 01: compile-time error
+  const String.fromEnvironment('NOT_FOUND', defaultValue: true); // //# 02: compile-time error
+  const String.fromEnvironment(null); // //# 03: compile-time error
+  const String.fromEnvironment(1); // //# 04: compile-time error
+  const String.fromEnvironment([]); // //# 05: compile-time error
 }