Resolve "prevent issues if hidden files are created inside the nitrile-packages directory"

What does this MR do?

This only prints paths with invalid metadata if some other error occurs, as proposed in the issue discussion.

I suggest releasing this as 0.4.22, as some users are struggling with this. Before releasing, I'd wait for !126 (merged) to be merged as well.

Changes to public APIs

Author's checklist (required)

• If the nitrile.yml format has changed, a migration has been defined in Nitrile.Package.Migrate
• A changelog entry has been added (guidelines)
• Newly added code is documented (guidelines)
• Newly added code has a style consistent with the rest of the repository
• Intermediate commits compile (use git rebase -i main if not)

Related issues

Closes #62 (closed)