Merge pull request #37108 from ktoso/wip-async_task_async_let_child_cancel-without-sleep

[Concurrency] Harden async_task_async_let_child_cancel so it does not need sleep

Author: ktoso

Diff for: test/Concurrency/Runtime/async_task_async_let_child_cancel.swift

@@ -18,6 +18,10 @@ func printWaitPrint(_ int: Int) async -> Int {
 
 @available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, *)
 func test() async {
+  let h = detach {
+    await printWaitPrint(0)
+  }
+
   let handle = detach {
     print("detached run, cancelled:\(Task.isCancelled)")
 
@@ -27,6 +31,8 @@ func test() async {
     async let two = printWaitPrint(2)
     print("spawned: 2")
 
+    h.cancel()
+
     let first = await one
     print("awaited: 1: \(first)")
     let second = await two
@@ -40,7 +46,7 @@ func test() async {
     print("exit detach")
   }
 
-  await Task.sleep(2 * 1_000_000)
+  await h.get()
 
   print("cancel")
   handle.cancel()