Fails if workspace contains a crate that is not yet published

[thomaseizinger]

See https://github.com/libp2p/rust-libp2p/actions/runs/6087635818/job/16516621765?pr=4248 for example.

This PR introduces a new crate which is not published yet. We would only publish it once the PR is merged. I think the action should ignore those until then.