Do not run hostname tests on macOS

- ports 522088b6be to this branch

src/Servers/Kestrel/shared/test/TransportTestHelpers/HostNameIsReachableAttribute.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Net;
 using System.Net.Sockets;
+using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Testing.xunit;
 
@@ -30,6 +31,12 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
 
         private async Task<bool> HostNameIsReachable()
         {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+            {
+                // Code below is unreliable on macOS and tests fail on that platform.
+                return false;
+            }
+
             try
             {
                 _hostname = Dns.GetHostName();