input: Write a python function to create and start multiple processes that print their process IDs.
  assert isinstance(start_processes(3), list)
  assert len(start_processes(3)) == 3
  assert all(isinstance(pid, int) for pid in start_processes(3))
output: import multiprocessing
  
  def worker():
      print(f"Process ID: {multiprocessing.current_process().pid}")
      return multiprocessing.current_process().pid
  
  def start_processes(n):
      processes = []
      for _ in range(n):
          process = multiprocessing.Process(target=worker)
          process.start()
          processes.append(process)
      pids = [p.pid for p in processes]
      for process in processes:
          process.join()
      return pids