Every time I create an experiment workspace, I forget that [`experiment_name` can't contain hyphens](https://freexian-team.pages.debian.net/debusine/reference/workflows/specs/create-experiment-workspace.html), which feels like a very unnatural restriction to me. I know that we construct the new workspace name by joining the base workspace name and the experiment name with a hyphen, which is probably where this restriction came from; but I don't think we rely on being able to decompose that again, so it shouldn't really matter. Could we perhaps add "-" to the list of valid characters here? /cc @enrico