Linux: using k4a API requires access to an X server

[jackjansen]

Migrated from https://gitlab.com/VRTogether_EU/cwipc/cwipc_kinect/-/issues/17

The k4a API doesn't work if it doesn't have access to the GPU (through OpenGL), not even for offline use.

microsoft/Azure-Kinect-Sensor-SDK#810 has some details, and links to various other issues with more information.
That issue also has some comments that the k4a maintainers plan to address this issue in a future release.

For us, this means that at the moment the CI/CD cannot run the test cases: docker container, therefore no X server. Same is true when logged into a machine with ssh (no DISPLAY variable, therefore no access to the X server).

The issue 810 linked above shows that all sorts of workarounds with trying to install a headless X server in the container don't work (too old OpenGL).

So for now I'll disable the tests on Linux unless DISPLAY is set. And when a new release of k4a is available we'll see.