Run workflows in IceCube containers

Created by: asogaard

By default, GitHub Actions workflow run on Ubuntu servers. This means that icetray and other IceCube packages are not available at runtime, and therefore repository code that uses these packages cannot be tested. However, it seems from here to be possible to run jobs in containers such as icecube:icetray. This would be very useful to increase the fraction of code that can be tested automatically.