Update VersionHelper.cs

Author: ghost1372

src/Shared/HandyControlDemo_Shared/Tools/Helper/VersionHelper.cs

@@ -40,6 +40,8 @@ internal static string GetVersion()
         var netVersion = ".NET 7.0";
 #elif NET8_0
         var netVersion = ".NET 8.0";
+#elif NET9_0
+        var netVersion = ".NET 9.0";
 #elif NETCOREAPP3_0
         var netVersion = ".NET CORE 3.0";
 #elif NETCOREAPP3_1