https://gitlab.xfce.org/apps/catfish/-/tags/catfish-4.20.0

Context: https://archlinux.org/todo/general-xfce-packages-rework/

- Use SPDX identifier for the license
- Switch to a more transparent source (git sources)
- Add nvchecker integration (.nvchecker.toml)

which used to be in [base] but the new metapackage no longer has it included.