[tests] Don't forcefully exit macOS tests. (#10844)

* [tests] Don't forcefully exit macOS tests.

Instead give the process a chance to exist (3 seconds), before we take drastic
measures.

* Bump Touch.Unit.

New commits in spouliot/Touch.Unit:

* spouliot/Touch.Unit@f19eb45 [TouchRunner] Try to make MacRunner exit nicely. (#100)

Diff: a33e0c3f2e..f19eb45cb6

* It looks like mono from 2020-02 doesn't want to exit no matter what, so limit this to .NET.

external/Touch.Unit

@@ -1 +1 @@
-Subproject commit a33e0c3f2e80f3ff2e2d9078a82a260b20d259a9
+Subproject commit f19eb45cb6439bc2bb03d467364b27867e346502

tests/common/mac/MacMain.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Runtime.InteropServices;
+using System.Threading;
 using System.Threading.Tasks;
 
 namespace Xamarin.Mac.Tests {
@@ -12,7 +13,24 @@ namespace Xamarin.Mac.Tests {
 			arguments.RemoveAll ((arg) => arg.StartsWith ("-psn_", StringComparison.Ordinal));
 
 			var exit_code = await MonoTouch.NUnit.UI.MacRunner.MainAsync (arguments, true, _exit, typeof (MainClass).Assembly);
+
+#if NET
+			var exit_monitor = new Thread (() =>
+			{
+				// Wait for 3 seconds
+				Thread.Sleep (3000);
+				// If we're still here, then something went wrong. Let's exit.
+				Console.WriteLine ($"The process didn't exist within 3s of returning from Main. Assuming something is deadlocked, and will now exit immediately and forcefully (with exit code {exit_code}).");
+				_exit (exit_code);
+			}) {
+				Name = "Exit monitor",
+				IsBackground = true,
+			};
+			exit_monitor.Start ();
+#else
 			_exit (exit_code);
+#endif
+
 			return exit_code;
 		}