Surpressing multi-threaded process warning from flake8.

[fujitatomoya]

Description

• before

root@tomoyafujita-B760M-Pro-RS-D4:~/ros2_ws/colcon_ws# colcon test --event-handlers console_direct+ --packages-select launch_testing_ros
Starting >>> launch_testing_ros
============================= test session starts ==============================
platform linux -- Python 3.12.3, pytest-7.4.4, pluggy-1.4.0
cachedir: /root/ros2_ws/colcon_ws/build/launch_testing_ros/.pytest_cache
rootdir: /root/ros2_ws/colcon_ws/src/ros2/launch_ros/launch_testing_ros
configfile: pytest.ini
testpaths: test
plugins: launch-testing-ros-0.29.6, launch-testing-3.9.6, ament-mypy-0.20.3, ament-xmllint-0.20.3, ament-copyright-0.20.3, ament-pep257-0.20.3, ament-flake8-0.20.3, ament-lint-0.20.3, launch-pytest-3.9.6, anyio-4.11.0, None-None, timeout-2.2.0, cov-4.1.0, rerunfailures-12.0, mock-3.12.0, colcon-core-0.20.1
collecting ...
collected 10 items

test/test_copyright.py .                                                 [ 10%]
test/test_flake8.py .                                                    [ 20%]
test/test_pep257.py .                                                    [ 30%]
test/test_xmllint.py .                                                   [ 40%]
test/examples/check_msgs_launch_test.py .                                [ 50%]
test/examples/check_node_launch_test.py .                                [ 60%]
test/examples/set_param_launch_test.py .                                 [ 70%]
[Processing: launch_testing_ros]
test/examples/talker_listener_launch_test.py .                           [ 80%]
test/examples/wait_for_topic_inject_trigger_test.py .                    [ 90%]
test/examples/wait_for_topic_launch_test.py .                            [100%]
- generated xml file: /root/ros2_ws/colcon_ws/build/launch_testing_ros/pytest.xml -
======================= 10 passed, 28 warnings in 35.01s =======================

=============================== warnings summary ===============================
test/test_flake8.py: 28 warnings
  Warning: This process (pid=898700) is multi-threaded, use of fork() may lead to deadlocks in the child.

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
--- stderr: launch_testing_ros

=============================== warnings summary ===============================
test/test_flake8.py: 28 warnings
  Warning: This process (pid=898700) is multi-threaded, use of fork() may lead to deadlocks in the child.

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
---
Finished <<< launch_testing_ros [36.2s]

Summary: 1 package finished [37.1s]

• after

root@tomoyafujita-B760M-Pro-RS-D4:~/ros2_ws/colcon_ws# colcon test --event-handlers console_direct+ --packages-select launch_testing_ros
Starting >>> launch_testing_ros
============================= test session starts ==============================
platform linux -- Python 3.12.3, pytest-7.4.4, pluggy-1.4.0
cachedir: /root/ros2_ws/colcon_ws/build/launch_testing_ros/.pytest_cache
rootdir: /root/ros2_ws/colcon_ws/src/ros2/launch_ros/launch_testing_ros
configfile: pytest.ini
testpaths: test
plugins: launch-testing-ros-0.29.6, launch-testing-3.9.6, ament-mypy-0.20.3, ament-xmllint-0.20.3, ament-copyright-0.20.3, ament-pep257-0.20.3, ament-flake8-0.20.3, ament-lint-0.20.3, launch-pytest-3.9.6, anyio-4.11.0, None-None, timeout-2.2.0, cov-4.1.0, rerunfailures-12.0, mock-3.12.0, colcon-core-0.20.1
collecting ...
collected 10 items

test/test_copyright.py .                                                 [ 10%]
test/test_flake8.py .                                                    [ 20%]
test/test_pep257.py .                                                    [ 30%]
test/test_xmllint.py .                                                   [ 40%]
test/examples/check_msgs_launch_test.py .                                [ 50%]
test/examples/check_node_launch_test.py .                                [ 60%]
test/examples/set_param_launch_test.py .                                 [ 70%]
[Processing: launch_testing_ros]
test/examples/talker_listener_launch_test.py .                           [ 80%]
test/examples/wait_for_topic_inject_trigger_test.py .                    [ 90%]
test/examples/wait_for_topic_launch_test.py .                            [100%]

- generated xml file: /root/ros2_ws/colcon_ws/build/launch_testing_ros/pytest.xml -
============================= 10 passed in 34.96s ==============================
Finished <<< launch_testing_ros [36.1s]

Summary: 1 package finished [37.0s]

Fixes # (issue)

Is this user-facing behavior change?

No

Did you use Generative AI?

No

Additional Information

[fujitatomoya]

@ahcorde can you review this?