C#: Add a RedundantToStringCall test case.

Author: michaelnebel

csharp/ql/test/query-tests/Useless Code/RedundantToStringCall/RedundantToStringCall.cs

@@ -9,5 +9,8 @@ public void M(object o)
 
         Console.WriteLine($"Hello: {o.ToString()}"); // BAD
         Console.WriteLine($"Hello: {o}"); // GOOD
+
+        Console.WriteLine("Hello: " + o.ToString()); // BAD
+        Console.WriteLine("Hello: " + o); // GOOD
     }
 }

csharp/ql/test/query-tests/Useless Code/RedundantToStringCall/RedundantToStringCall.expected

@@ -1,3 +1,4 @@
 | RedundantToStringCall.cs:7:27:7:38 | call to method ToString | Redundant call to 'ToString' on a String object. |
 | RedundantToStringCall.cs:10:37:10:48 | call to method ToString | Redundant call to 'ToString' on a String object. |
+| RedundantToStringCall.cs:13:39:13:50 | call to method ToString | Redundant call to 'ToString' on a String object. |
 | RedundantToStringCallBad.cs:7:45:7:56 | call to method ToString | Redundant call to 'ToString' on a String object. |