update usings

Author: AntPolkanov

docs/quickstart/server.mdx

@@ -1506,7 +1506,7 @@ Next, define a class with the tool execution handlers for querying and convertin
 ```csharp
 using ModelContextProtocol.Server;
 using System.ComponentModel;
-using System.Net.Http.Json;
+using System.Globalization;
 using System.Text.Json;
 
 namespace QuickstartWeatherServer.Tools;