Follow-up to https://github.com/zed-industries/zed/pull/24278

This PR ensures we're checking if there's a license-type file in both US
& UK English spelling, and fixes the error logging again, treating for
when the worktree contains just a single file or multiple.

Release Notes:

- N/A

Co-authored-by: Bennet Bo Fenner <53836821+bennetbo@users.noreply.github.com>