[ls] return unresolved packages as a warning instead of an error

[Lagoja]

Summary

Fixes #2510

Previously, devbox ls --outdated would error on packages that it could not resolve, like stdenv.cc.cc.lib or darwin.apple_sdk.frameworks.IOKit. This prevented devbox from checking if the rest of the packages were outdated.

This PR changes the error to a warning, so the rest of the version checks can proceed

How was it tested?

1. Create a devbox.json
2. Add standard packages using devbox add
3. Add stdenv.cc.cc.lib or darwin.apple_sdk.frameworks.IOKit to the project
4. Verify that devbox ls --outdated shows a warning for the non-versioned packages instead of an error.