Make sure the threaded and non-threaded API is easily distinguishable

Author: shana

src/GitHub.Api/Tasks/TaskBase.cs

@@ -24,7 +24,7 @@ public interface ITask : IAsyncResult
         /// <summary>
         /// Run a callback at the end of the task execution, on a separate thread, regardless of execution state
         /// </summary>
-        ITask Finally(Action<bool, Exception> actionToContinueWith, TaskAffinity affinity = TaskAffinity.Concurrent);
+        ITask Finally(Action<bool, Exception> actionToContinueWith, TaskAffinity affinity);
         /// <summary>
         /// Run another task at the end of the task execution, on a separate thread, regardless of execution state
         /// </summary>

src/tests/TaskSystemIntegrationTests/Tests.cs

@@ -600,7 +600,9 @@ public async Task StartAndEndAreAlwaysRaised()
             ITask task = new ActionTask(Token, _ => { throw new Exception(); });
             task.OnStart += _ => runOrder.Add("start");
             task.OnEnd += (_, __, ___) => runOrder.Add("end");
-            task = task.Finally((_, __) => {});
+            // we want to run a Finally on a new task (and not in-thread) so that the StartAndSwallowException handler runs after this
+            // one, proving that the exception is propagated after everything is done
+            task = task.Finally((_, __) => {}, TaskAffinity.Concurrent);
 
             await task.StartAndSwallowException();
             CollectionAssert.AreEqual(new string[] { "start", "end" }, runOrder);