radv/ci: disable unstable/always-failing jobs
In an effort to reduce the difficulty of monitoring CI failures, I would like to first reduce the amount of failures.
Polaris10 has been extremely unstable, and has been an enormous source of noise. So let's disable it until we figure out how to make context creation stable.
Kabini is running low on RAM, and fails to run vkd3d... so let's also disable that.