fix: forc build panic when sway package folder contains dot

[Halimao]

Description

Close #5434

Since canonical_manifest_dir is a dir, not a file, to get the last-level dir name, we should use file_name() instead of file_stem.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[kayagokalp]

Thanks for the PR @Halimao, great catch! Can we add a test as @crodas mentioned? I added couple of options where to place it in that review

[Halimao]

Thanks for the PR @Halimao, great catch! Can we add a test as @crodas mentioned? I added couple of options where to place it in that review

@kayagokalp Addressed

[kayagokalp]

Thanks!