update to FFmpeg 6.0

[fanyj]

Is your feature request related to a problem? Please describe.
I'm using this awesome repo to normalize audio files in my project, and I've encountered a bug in FFmpeg 5.0 where the loudnorm filter does not seem to work for short audio files (about 3 seconds).
Here is the related issue.

Describe the solution you'd like
This issue has been fixed in FFmpeg v6.0, so it would be great if we could update FFmpeg to 6.0.

Describe alternatives you've considered
I've checked the Custom Build Guide but haven't found how to bump the FFmpeg version. Does it work if I just change the FFMPEG_VERSION value?

[fanyj]

For anyone who encounters the same issue, please update the ENV FFMPEG_VERSION=n6.0.1 in the Dockerfile and execute make prd-mt. After the compilation is complete, you can found the output files in the path ./packages/core-mt