Include omission from previous PR

[planetis-m]

I accidentally missed the following change from my previous PR:

recvIso is also made to use Isolated[T] directly as this fixes receiving ref objects.

Meaning this now compiles:

type
  Foo = ref object
    data: int

var chan = newChan[Foo]()

block example_blocking:
  # This proc will be run in another thread.
  proc basicWorker() =
    chan.send(Foo(data: 4))

  # Launch the worker.
  var worker: Thread[void]
  createThread(worker, basicWorker)

  # Block until the message arrives, then print it out.
  var dest: Isolated[Foo]
  dest = chan.recvIso()
  echo dest.extract().data

  # Wait for the thread to exit before moving on to the next example.
  worker.joinThread()