You were looking at an old version of the voxl2)_io driver. The latest version can be found here : https://github.com/modalai/px4-firmware/blob/voxl-dev/src/drivers/voxl2_io/voxl2_io.cpp
Voxl2IO::get_version_info() function will query the hardware and software version of the M0065 board before the voxl2_io px4 module will successfully start up and send out control commands.
The version check will make your testing slightly more complicated because you'd need to implement the extended version reply on your STM. You should also check whether the actual format of the commands that you implemented is correct (not from the old version).
If you are able to compile the px4 code, you can just disable the version check in the code and the voxl2_io px4 module should let you send out the actuator commands.
Let me know if you need more assistance.
Alex