Code review comment for ~barryprice/charm-k8s-discourse/+git/charm-k8s-discourse:v2.8.0.beta7-20.04

I think there's been a change in charmcraft which means the "build" directory is no longer used as before (it's now used in a way similar to snapcraft).

As a result I think you'll want something like this https://pastebin.ubuntu.com/p/kkx5d6Pgf2/ - essentially just adding `{toxinidir}/lib` to the testenv path. Fwiw, Jon Seager's teams will be standardising on a tox.ini similar to this https://github.com/jnsgruk/charm-kubernetes-dashboard/blob/main/tox.ini. I'm not saying we should change to this exactly, but it shows `{toxinidir}/lib` as part of testenv.