Fix warnings_checker.dart handling of multitests

tests/corelib_strong/bool_from_environment2_test.dart

Index: tests/corelib_strong/bool_from_environment2_test.dart
diff --git a/tests/corelib_strong/bool_from_environment2_test.dart b/tests/corelib_strong/bool_from_environment2_test.dart
index 0e6d410687e14534fda67588ac766f8b6b54bb01..0329c544611e2aa0633037b392a5d5126254ef1f 100644
--- a/tests/corelib_strong/bool_from_environment2_test.dart
+++ b/tests/corelib_strong/bool_from_environment2_test.dart
@@ -3,9 +3,9 @@
 // BSD-style license that can be found in the LICENSE file.
 
 main() {
-  const bool.fromEnvironment('NOT_FOUND', defaultValue: ''); // /// 01: compile-time error
-  const bool.fromEnvironment('NOT_FOUND', defaultValue: 1); // /// 02: compile-time error
-  const bool.fromEnvironment(null); // /// 03: compile-time error
-  const bool.fromEnvironment(1); // /// 04: compile-time error
-  const bool.fromEnvironment([]); // /// 05: compile-time error
+  const bool.fromEnvironment('NOT_FOUND', defaultValue: ''); // //# 01: compile-time error
+  const bool.fromEnvironment('NOT_FOUND', defaultValue: 1); // //# 02: compile-time error
+  const bool.fromEnvironment(null); // //# 03: compile-time error
+  const bool.fromEnvironment(1); // //# 04: compile-time error
+  const bool.fromEnvironment([]); // //# 05: compile-time error
 }