In cases when a given GUI app is absent (encountered when excluding
packages like `cosmic-term`, etc), the test fails because the GUI app
doesn't launch. That, while being a failure, is not connected to the
COSMIC DE itself. So if a binary is missing, skip launch-testing it.
The NixOS tests for COSMIC fail on `aarch64-linux`. So far, this points
to virgl/opengl not working properly on aarch64+qemu but we don't
enable 3D acceleration on `x86_64-linux` either.
Regardless, this means that tests on `aarch64-linux` that are failing,
are not failing early enough and become a 15 minute (900 seconds is the
default timeout) resource hog on Ofborg and Hydra. A temporary way
around this problem is to introduce shorter timeouts than the default of
900 seconds.
