Add documentation to ExecuteScalar method stub

Co-authored-by: johlju <7189721+johlju@users.noreply.github.com>

Author: Copilot

tests/Unit/Stubs/SMO.cs

@@ -1332,6 +1332,8 @@ public class ServerConnection
         public void Create()
         {}
 
+        // Method: ExecuteScalar
+        // Used for testing scalar query execution in Invoke-SqlDscScalarQuery
         public object ExecuteScalar(string query)
         {
             return null;