Samples: Refactors typeof(T) to input.GetType() on CosmosSystemTextJsonSerializer (#3452)

Co-authored-by: Nalu Tripician <ntripician@microsoft.com>

Microsoft.Azure.Cosmos.Samples/Usage/SystemTextJson/CosmosSystemTextJsonSerializer.cs

@@ -40,7 +40,7 @@
         public override Stream ToStream<T>(T input)
         {
             MemoryStream streamPayload = new MemoryStream();
-            this.systemTextJsonSerializer.Serialize(streamPayload, input, typeof(T), default);
+            this.systemTextJsonSerializer.Serialize(streamPayload, input, input.GetType(), default);
             streamPayload.Position = 0;
             return streamPayload;
         }