commnity/ristretto: Feature Request: file-dev makedepends

This change compiles Ristretto with libmagic magic number filetype detection, which can improve UX when dealing with images that are mislabeled, not labeled, etc.

Tested and compiled locally and works well and fixed a few images I've received that were wrong-extension that would cause Ristretto to complain about wrong magic number.

If it is desired, I can open an MR with this tweak to the APKBUILD.