Should skip if no baseline versions available

[maschad]

Describe your use case

Currently, if one is running this in CI across multiple packages in a workspace, it would be helpful to ignore errors resulting from packages without a baseline version as they could be new crates.

Describe the solution you'd like

Skip checks (akin to major version bumps) if no baseline version is available.

[obi1kenobi]

Another use case for this is in https://github.com/hyperium/tonic where there are multiple crates that are intended for testing purposes only and are not published anywhere.

[thomaseizinger]

Another use case for this is in hyperium/tonic where there are multiple crates that are intended for testing purposes only and are not published anywhere.

We solve that by not running for crates that have publish set to false:

https://github.com/libp2p/rust-libp2p/blob/e0ab8cd3d577fdfcda7947d27b1df43b0a41d3bd/.github/workflows/ci.yml#L242-L252