d/tests: Log debug messages
d/tests: Mark gnome-desktop-testing to be skipped if not installable
If gnome-desktop-testing isn't available, we want to treat that as though this test had been skipped, rather than as though it had failed. d/tests/run effectively duplicates it anyway.
debian: Enable Gitlab-CI
We are targeting scout, but because scout is so old, its SDK environment is too old to run deb-build-snapshot. Instead, we do that step in a Debian 10 'buster' environment, and hand over the artifacts from that to the autopkgtest step.
Our build-dependencies are not all preinstalled in the CI Docker images, so add them.