tests_python/test_utilities.py::test_find_main_thread_id fails #284

This test has started failing on Debian with both Python 3.11 and Python 3.12 (pydevd version 2.9.6 and 3.1.0) on the assertion assert 'threading' not in sys.modules on line 27 of tests_python/resources/_pydevd_test_find_main_thread_id.py. I don't know why it should be imported; it is imported by subprocess, but this should be running in a fresh thread.