Fix warnings_checker.dart handling of multitests

tests/language/super_conditional_operator_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Verify that the ?. operator cannot be used with "super".
 
 class B {
   B();
   B.namedConstructor();
   var field = 1;
   method() => 1;
 }
 
 class C extends B {
   C()
-    : super?.namedConstructor() /// 01: compile-time error
+    : super?.namedConstructor() //# 01: compile-time error
   ;
 
   test() {
-    super?.field = 1; /// 02: compile-time error
-    super?.field += 1; /// 03: compile-time error
-    super?.field ??= 1; /// 04: compile-time error
-    super?.field; /// 05: compile-time error
-    1 * super?.field; /// 06: compile-time error
-    -super?.field; /// 07: compile-time error
-    ~super?.field; /// 08: compile-time error
-    !super?.field; /// 09: compile-time error
-    --super?.field; /// 10: compile-time error
-    ++super?.field; /// 11: compile-time error
-    super?.method(); /// 12: compile-time error
-    1 * super?.method(); /// 13: compile-time error
-    -super?.method(); /// 14: compile-time error
-    ~super?.method(); /// 15: compile-time error
-    !super?.method(); /// 16: compile-time error
-    --super?.method(); /// 17: compile-time error
-    ++super?.method(); /// 18: compile-time error
+    super?.field = 1; //# 02: compile-time error
+    super?.field += 1; //# 03: compile-time error
+    super?.field ??= 1; //# 04: compile-time error
+    super?.field; //# 05: compile-time error
+    1 * super?.field; //# 06: compile-time error
+    -super?.field; //# 07: compile-time error
+    ~super?.field; //# 08: compile-time error
+    !super?.field; //# 09: compile-time error
+    --super?.field; //# 10: compile-time error
+    ++super?.field; //# 11: compile-time error
+    super?.method(); //# 12: compile-time error
+    1 * super?.method(); //# 13: compile-time error
+    -super?.method(); //# 14: compile-time error
+    ~super?.method(); //# 15: compile-time error
+    !super?.method(); //# 16: compile-time error
+    --super?.method(); //# 17: compile-time error
+    ++super?.method(); //# 18: compile-time error
   }
 }
 
 main() {
   new C().test();
 }