Tests: add OS to output

Trying to figure out what's happening with Appveyor vs. local socket exceptions.

StackExchange.Redis.Tests/Helpers/Extensions.cs

-using Xunit.Abstractions;
+using System.Runtime.InteropServices;
+using Xunit.Abstractions;
 
 namespace StackExchange.Redis.Tests.Helpers
 {
@@ -15,6 +16,7 @@ public static void WriteFrameworkVersion(this ITestOutputHelper output)
 #else
             output.WriteLine("Compiled under <unknown framework>");
 #endif
+            output.WriteLine("Running on: " + RuntimeInformation.OSDescription);
         }
     }
 }

StackExchange.Redis.Tests/StackExchange.Redis.Tests.csproj

@@ -18,6 +18,7 @@
     <PackageReference Include="Jil" Version="2.15.4" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
     <PackageReference Include="Moq" Version="4.7.99" />
+    <PackageReference Include="System.Runtime.InteropServices.RuntimeInformation" Version="4.3.0" />
     <PackageReference Include="xunit" Version="$(xUnitVersion)" />
     <PackageReference Include="xunit.runner.visualstudio" Version="$(xUnitVersion)" />
     <DotNetCliToolReference Include="dotnet-xunit" Version="$(xUnitVersion)" />