speech: add awful hack around Python threading problem

[peterbarker]

MAV> Detected vehicle 1:1 on link 0
Using speech backend 'speechd'
Traceback (most recent call last):
  File "/usr/lib/python3.10/multiprocessing/queues.py", line 244, in _feed
    obj = _ForkingPickler.dumps(obj)
  File "/usr/lib/python3.10/multiprocessing/reduction.py", line 51, in dumps
    cls(buf, protocol).dump(obj)
  File "/usr/lib/python3.10/multiprocessing/connection.py", line 968, in reduce_connection
    df = reduction.DupFd(conn.fileno())
  File "/usr/lib/python3.10/multiprocessing/connection.py", line 170, in fileno
    self._check_closed()
  File "/usr/lib/python3.10/multiprocessing/connection.py", line 136, in _check_closed
    raise OSError("handle is closed")
OSError: handle is closed