Also build docker image for arm64

[karuboniru]

so people can run this in their rpi

[URenko]

I noticed "Add libjxl support once in stable" is in the TODO list of https://github.com/wader/static-ffmpeg/blob/master/README.md
I'm afraid we need to wait it or choose another build.

[karuboniru]

Now we get fffmpeg w/ libjxl

[URenko]

Excellent!