THRIFT-5407: Minor changes in .NET to support netcoreapp3.1
Client: netstd
Patch: Mario Emmenlauer

This closes #2384
diff --git a/test/netstd/Server/Program.cs b/test/netstd/Server/Program.cs
index 0052bce..8f1f36d 100644
--- a/test/netstd/Server/Program.cs
+++ b/test/netstd/Server/Program.cs
@@ -18,6 +18,7 @@
 using System;
 using System.Linq;
 using System.Collections.Generic;
+using System.Runtime.InteropServices;
 using ThriftTest;
 
 namespace Server
@@ -26,7 +27,7 @@
     {
         public static int Main(string[] args)
         {
-            if (OperatingSystem.IsWindows())
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
             {
                 try
                 {
@@ -65,5 +66,3 @@
         }
     }
 }
-
-
diff --git a/test/netstd/Server/Server.csproj b/test/netstd/Server/Server.csproj
index fe1c394..e2ec93c 100644
--- a/test/netstd/Server/Server.csproj
+++ b/test/netstd/Server/Server.csproj
@@ -20,6 +20,7 @@
 
   <PropertyGroup>
     <TargetFramework>net5.0</TargetFramework>
+    <LangVersion>9.0</LangVersion>
     <AssemblyName>Server</AssemblyName>
     <PackageId>Server</PackageId>
     <OutputType>Exe</OutputType>