Update ffmpeg to a more recent build to fix Dolby Atmos remuxing

One of my main uses of a-shell is remuxing mkv movies to mp4 via iOS shortcuts so I can airplay them natively to Apple TV.

(happy to share the shortcut if anyone is interested)

Problem: ffmpeg builds older than April/May 2025 strip Dolby Atmos metadata while creating the mp4 container. This has been fixed in newer builds.

Fix: Please, may I politely request that you update the included ffmpeg to a more recent codebase so I can remux Atmos files on iOS instead of needing to use my Mac.

Thanks for your time and for making this exceptionally useful app.