ROS2 build process for a CPP package is using a different Python version

Question

I am using ROS2 on Windows. I am trying to build my my_robot_cpp package using colcon build. However, I get this error:

C:\Users\ken\ROS2\ros2_ws>colcon build --event-handlers desktop_notification-
Starting >>> my_robot_controller
Starting >>> my_robot_cpp
Finished <<< my_robot_controller [1.38s]
--- stderr: my_robot_cpp
Traceback (most recent call last):
  File "C:\dev\ros2_humble\share\ament_cmake_core\cmake\core\package_xml_2_cmake.py", line 22, in <module>
    from catkin_pkg.package import parse_package_string
ModuleNotFoundError: No module named 'catkin_pkg'
CMake Error at C:/dev/ros2_humble/share/ament_cmake_core/cmake/core/ament_package_xml.cmake:95 (message):

  execute_process(C:/Users/ken/AppData/Local/Programs/Python/Python39/python.exe
  C:/dev/ros2_humble/share/ament_cmake_core/cmake/core/package_xml_2_cmake.py
  C:/Users/ken/ROS2/ros2_ws/src/my_robot_cpp/package.xml
  C:/Users/ken/ROS2/ros2_ws/build/my_robot_cpp/ament_cmake_core/package.cmake)
  returned error code 1
Call Stack (most recent call first):
  C:/dev/ros2_humble/share/ament_cmake_core/cmake/core/ament_package_xml.cmake:49 (_ament_package_xml)
  C:/dev/ros2_humble/share/ament_lint_auto/cmake/ament_lint_auto_find_test_dependencies.cmake:31 (ament_package_xml)
  CMakeLists.txt:23 (ament_lint_auto_find_test_dependencies)

---
Failed   <<< my_robot_cpp [2.12s, exited with code 1]

Summary: 1 package finished [2.41s]
  1 package failed: my_robot_cpp
  1 package had stderr output: my_robot_cpp

I see the error ModuleNotFoundError: No module named 'catkin_pkg' so I attempt to install it, but it says it is already installed:

C:\Users\ken\ROS2\ros2_ws>pip install -U catkin_pkg
Requirement already satisfied: catkin_pkg in c:\python38\lib\site-packages (0.5.2)
Collecting catkin_pkg
  Obtaining dependency information for catkin_pkg from https://files.pythonhosted.org/packages/91/f7/86d933ec31f00450f513ef110fa9c0e5da4c6e2c992933a35c8d8fe7d01f/catkin_pkg-1.0.0-py3-none-any.whl.metadata
  Downloading catkin_pkg-1.0.0-py3-none-any.whl.metadata (1.3 kB)
Requirement already satisfied: docutils in c:\python38\lib\site-packages (from catkin_pkg) (0.20.1)
Requirement already satisfied: python-dateutil in c:\python38\lib\site-packages (from catkin_pkg) (2.8.2)
Requirement already satisfied: pyparsing in c:\python38\lib\site-packages (from catkin_pkg) (2.4.7)
Requirement already satisfied: setuptools in c:\python38\lib\site-packages (from catkin_pkg) (41.2.0)
Requirement already satisfied: six>=1.5 in c:\python38\lib\site-packages (from python-dateutil->catkin_pkg) (1.16.0)
Downloading catkin_pkg-1.0.0-py3-none-any.whl (75 kB)
   ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 76.0/76.0 kB 2.1 MB/s eta 0:00:00
Installing collected packages: catkin_pkg
  Attempting uninstall: catkin_pkg
    Found existing installation: catkin-pkg 0.5.2
    Uninstalling catkin-pkg-0.5.2:
      Successfully uninstalled catkin-pkg-0.5.2
Successfully installed catkin_pkg-1.0.0

The issue I see now I believe is that that the catkin_pkg module is installed for Python 3.8, yet the command appears to be trying to use a different Python version (3.9) as evident in this line: execute_process(C:/Users/ken/AppData/Local/Programs/Python/Python39/python.exe

I also attempted to set the PYTHON_EXECUTABLE variable in the CMakeLists.txt file but it doesn't seem to do anything.

# Set the path to your Python executable
set(PYTHON_EXECUTABLE /C:/Python38/python.exe)

cmake_minimum_required(VERSION 3.8)
project(my_robot_cpp)

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

# find dependencies
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)

if(BUILD_TESTING)
  find_package(ament_lint_auto REQUIRED)
  set(ament_cmake_copyright_FOUND TRUE)
  set(ament_cmake_cpplint_FOUND TRUE)
  ament_lint_auto_find_test_dependencies()
endif()

ament_package()

I saw this question already, it's similar to my problem however I didn't get any help.

Also, I checked the install\local_setup.bat file and it seems to be using the correct python executable so i really dont know where it is wrong.

:_colcon_run_ordered_commands
  setlocal enabledelayedexpansion
  :: check environment variable for custom Python executable
  if "%COLCON_PYTHON_EXECUTABLE%" NEQ "" (
    if not exist "%COLCON_PYTHON_EXECUTABLE%" (
      echo error: COLCON_PYTHON_EXECUTABLE '%COLCON_PYTHON_EXECUTABLE%' doesn't exist
      exit /b 1
    )
    set "_colcon_python_executable=%COLCON_PYTHON_EXECUTABLE%"
  ) else (
    :: use the Python executable known at configure time
    set "_colcon_python_executable=c:\python38\python.exe"
    :: if it doesn't exist try a fall back
    if not exist "!_colcon_python_executable!" (
      python --version > NUL 2> NUL
      if errorlevel 1 (
        echo error: unable to find python executable
        exit /b 1
      )
      set "_colcon_python_executable=python"
    )
  )