Test `advanced_spawner` tests are flaky

[christophfroehlich]

Describe the bug
#2895 introduced a new flaky test

2026-02-27T04:02:31.6714917Z     [  FAILED  ] TestLoadController.advanced_spawner_test_failed_activation_of_controllers
2026-02-27T04:02:31.6716011Z     
2026-02-27T04:02:31.6716397Z      1 FAILED TEST
2026-02-27T04:02:31.6716872Z     -- run_test.py: return code 1
2026-02-27T04:02:31.6719103Z     -- run_test.py: inject classname prefix into gtest result file '/home/runner/work/ros2_control_ci/ros2_control_ci/.work/target_ws/build/controller_manager/test_results/controller_manager/test_advanced_spawner.gtest.xml'
2026-02-27T04:02:31.6721417Z     -- run_test.py: verify result file '/home/runner/work/ros2_control_ci/ros2_control_ci/.work/target_ws/build/controller_manager/test_results/controller_manager/test_advanced_spawner.gtest.xml'
2026-02-27T04:02:31.6723009Z   >>>
2026-02-27T04:02:31.6723830Z build/controller_manager/test_results/controller_manager/test_advanced_spawner.gtest.xml: 21 tests, 0 errors, 1 failure, 0 skipped
2026-02-27T04:02:31.6725051Z - controller_manager.TestLoadController advanced_spawner_test_failed_activation_of_controllers
2026-02-27T04:02:31.6725757Z   <<< failure message
2026-02-27T04:02:31.6726698Z     /home/runner/work/ros2_control_ci/ros2_control_ci/.work/target_ws/src/ros-controls/ros2_control/controller_manager/test/test_advanced_spawner.cpp:864
2026-02-27T04:02:31.6728070Z     Expected equality of these values:
2026-02-27T04:02:31.6728512Z       cm_->get_loaded_controllers().size()
2026-02-27T04:02:31.6728918Z         Which is: 2
2026-02-27T04:02:31.6729270Z       3ul
2026-02-27T04:02:31.6729524Z         Which is: 3
2026-02-27T04:02:31.6729789Z   >>>

To Reproduce
ros-controls/ros2_control_ci#673

[christophfroehlich]

#3072

2026-03-04T04:35:56.1343981Z     [  FAILED  ] TestLoadController.advanced_spawner_unload_on_kill
2026-03-04T04:35:56.1344744Z     
2026-03-04T04:35:56.1345026Z      1 FAILED TEST
2026-03-04T04:35:56.1345387Z     -- run_test.py: return code 1
2026-03-04T04:35:56.1347127Z     -- run_test.py: inject classname prefix into gtest result file '/home/runner/work/ros2_control/ros2_control/.work/target_ws/build/controller_manager/test_results/controller_manager/test_advanced_spawner.gtest.xml'
2026-03-04T04:35:56.1349433Z     -- run_test.py: verify result file '/home/runner/work/ros2_control/ros2_control/.work/target_ws/build/controller_manager/test_results/controller_manager/test_advanced_spawner.gtest.xml'
2026-03-04T04:35:56.1350640Z   >>>
2026-03-04T04:35:56.1351616Z build/controller_manager/test_results/controller_manager/test_advanced_spawner.gtest.xml: 21 tests, 0 errors, 1 failure, 0 skipped
2026-03-04T04:35:56.1352982Z - controller_manager.TestLoadController advanced_spawner_unload_on_kill (/home/runner/work/ros2_control/ros2_control/.work/target_ws/src/ros2_control/controller_manager/test/test_advanced_spawner.cpp:459)
2026-03-04T04:35:56.1354242Z   <<< failure message
2026-03-04T04:35:56.1355542Z     /home/runner/work/ros2_control/ros2_control/.work/target_ws/src/ros2_control/controller_manager/test/test_advanced_spawner.cpp:474
2026-03-04T04:35:56.1356439Z     Expected equality of these values:
2026-03-04T04:35:56.1356872Z       cm_->get_loaded_controllers().size()
2026-03-04T04:35:56.1357303Z         Which is: 1
2026-03-04T04:35:56.1357610Z       0ul
2026-03-04T04:35:56.1357877Z         Which is: 0
2026-03-04T04:35:56.1358167Z   >>>

[saikishor]

The unload_on_kill is something that happens on the standard spawner. I'll try to take a look to improve it