Fix for the issue #3646. It looks like the default for macos and python 3.8+...

# TestDataMan1D.py: test for 1D data transfer by reading in Python

#  Created on: March 3, 2023

#      Author: Dmitry Ganyushin ganyushindi@ornl.gov

from multiprocessing import Process

import multiprocessing

import unittest

import numpy as np

import adios2

    def test_run(self):

        s = Process(target=self.thread_send)

        r = Process(target=self.thread_receive)

        s = multiprocessing.Process(target=self.thread_send)

        r = multiprocessing.Process(target=self.thread_receive)

        s.start()

        r.start()

if __name__ == '__main__':

    multiprocessing.set_start_method("fork")

    unittest.main()