Missing dependency on ament_cmake_flake8?

[130s]

Issue report

Required Info:

• Operating System: humble
• Installation type: Bin
• Version or commit hash:

  # ros2 pkg xml rosidl_generator_py                                                  
  <package format="3">
    <name>rosidl_generator_py</name>
    <version>0.18.0</version>
  

Steps to reproduce issue

Buildfarm output https://build.ros2.org/job/Rpr__smach__ubuntu_jammy_amd64/2/console for ros/executive_smach#112 where a dependency on ament_cmake_flake8 is removed in a downstream package (smach_msgs) so that none of the packages in the repo in the PR depends on nor call ament_cmake_flake8 any more.

(I haven't figured out exactly what command was called when the reported error occured. My guess is either some sort of `rosidl` command was called, or `colcon build`

:
17:32:59 -- Found PythonExtra: .so  
17:32:59 CMake Error at /opt/ros/rolling/share/rosidl_generator_py/cmake/rosidl_generator_py_generate_interfaces.cmake:335 (find_package):
17:32:59   By not providing "Findament_cmake_flake8.cmake" in CMAKE_MODULE_PATH this
17:32:59   project has asked CMake to find a package configuration file provided by
17:32:59   "ament_cmake_flake8", but CMake did not find one.
17:32:59 
17:32:59   Could not find a package configuration file provided by
17:32:59   "ament_cmake_flake8" with any of the following names:
17:32:59 
17:32:59     ament_cmake_flake8Config.cmake
17:32:59     ament_cmake_flake8-config.cmake
17:32:59 
17:32:59   Add the installation prefix of "ament_cmake_flake8" to CMAKE_PREFIX_PATH or
17:32:59   set "ament_cmake_flake8_DIR" to a directory containing one of the above
17:32:59   files.  If "ament_cmake_flake8" provides a separate development package or

Expected behavior

In a downstream interface package, no error during cmake regarding ament_cmake_flake8Config.cmake / ament_cmake_flake8-config.cmake should be seen while building rosidl package, even when the downstream interface package does NOT explicitly depend on ament_cmake_flake8.

Actual behavior

The error posted in "Steps to reproduce issue" section occurs.

[130s]

In ver 0.19.0, ament_cmake_flake8 IS find_package-ed when ADD_LINTER_TESTS is enabled, which is true in the case of ros/executive_smach#112 so failure occurring in that pkg makes sense.

https://github.com/ros2/rosidl_python/blob/0.19.0/rosidl_generator_py/cmake/rosidl_generator_py_generate_interfaces.cmake#L335