Fix race condition in Hosting test

Change Task.Delay(1) to Task.Yield() to avoid a super race condition.

Fix dotnet#43389

src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Internal/HostTests.cs

@@ -1372,7 +1372,7 @@ private class AsyncThrowingService : BackgroundService
         {
             protected override async Task ExecuteAsync(CancellationToken stoppingToken)
             {
-                await Task.Delay(1);
+                await Task.Yield();
 
                 throw new Exception("Background Exception");
             }