[4.1.x] Fixed #33719 -- Fixed test command crash when running in parallel.

Thanks Pēteris Caune for the report.

Regression in 3b3f38b3b0.
Backport of 41c4cb253c from main

tests/runtests.py

@@ -11,7 +11,6 @@ import subprocess
 import sys
 import tempfile
 import warnings
-from functools import partial
 from pathlib import Path
 
 try:
@@ -26,7 +25,7 @@ else:
     from django.core.exceptions import ImproperlyConfigured
     from django.db import connection, connections
     from django.test import TestCase, TransactionTestCase
-    from django.test.runner import _init_worker, get_max_test_processes, parallel_type
+    from django.test.runner import get_max_test_processes, parallel_type
     from django.test.selenium import SeleniumTestCaseBase
     from django.test.utils import NullTimeKeeper, TimeKeeper, get_runner
     from django.utils.deprecation import RemovedInDjango50Warning
@@ -401,11 +400,8 @@ def django_tests(
             parallel = 1
 
     TestRunner = get_runner(settings)
-    TestRunner.parallel_test_suite.init_worker = partial(
-        _init_worker,
-        process_setup=setup_run_tests,
-        process_setup_args=process_setup_args,
-    )
+    TestRunner.parallel_test_suite.process_setup = setup_run_tests
+    TestRunner.parallel_test_suite.process_setup_args = process_setup_args
     test_runner = TestRunner(
         verbosity=verbosity,
         interactive=interactive,