[CI] Humble source build fails

[christophfroehlich]

The humble source build on humble branch fails for some time now: https://github.com/ros-controls/ros2_controllers/actions/workflows/humble-source-build.yml?query=branch%3Ahumble

But the scheduled one (tagged with branch=master) succeeds?

ERROR:colcon.colcon_core.entry_point:Exception loading extension 'colcon_core.environment_variable.powershell_command': cannot import name 'OVERRIDE_OPT' from 'em' (/usr/local/bin/em.py) The Python package 'empy' must be installed and 'em' must not be installed since both packages share the same namespace Traceback (most recent call last): File "/usr/local/lib/python3.10/dist-packages/colcon_core/entry_point.py", line 120, in load_entry_points extension_type = load_entry_point(entry_point) File "/usr/local/lib/python3.10/dist-packages/colcon_core/entry_point.py", line 168, in load_entry_point return entry_point.load() File "/usr/local/lib/python3.10/dist-packages/pkg_resources/init.py", line 2465, in load return self.resolve() File "/usr/local/lib/python3.10/dist-packages/pkg_resources/init.py", line 2471, in resolve module = import(self.module_name, fromlist=['name'], level=0) File "/usr/local/lib/python3.10/dist-packages/colcon_powershell/shell/powershell.py", line 17, in from colcon_core.shell.template import expand_template File "/usr/local/lib/python3.10/dist-packages/colcon_core/shell/template/init.py", line 19, in raise e from None File "/usr/local/lib/python3.10/dist-packages/colcon_core/shell/template/init.py", line 10, in from em import OVERRIDE_OPT ImportError: cannot import name 'OVERRIDE_OPT' from 'em' (/usr/local/bin/em.py) The Python package 'empy' must be installed and 'em' must not be installed since both packages share the same namespace