Github actions: arm64-rpi image

[openoms]

Done in https://github.com/openoms/joininbox/pull/89

There is one issue where the sha256sum of the image did not match the image: https://github.com/openoms/joininbox/actions/runs/2770754146/attempts/1

sha256sum -c joininbox-arm64-rpi.img.sha256 
joininbox-arm64-rpi.img: FAILED
sha256sum: WARNING: 1 computed checksum did NOT match

sha256sum joininbox-arm64-rpi.img
520ddddf8cd61997829f52cc89a7aba8c8eca4ee50e5b637eeb1da89a2effb39  joininbox-arm64-rpi.img
cat joininbox-arm64-rpi.img.sha256 
bc8fdebde4dc3998fd2cc5b32377444f5e2a2c74b87efafef09d6daecf171255	joininbox-arm64-rpi.img

It is because the image is manipulated after the hash is created:

-rw-rw-r-- 1 s s 8589934592 Jul 31 20:56 joininbox-arm64-rpi.img
-rw-rw-r-- 1 s s         89 Jul 31 20:54 joininbox-arm64-rpi.img.sha256

Might be because of keep_input_artifact = true fixing in: https://github.com/openoms/joininbox/commit/fcbada861e3f50d7f339934a16314905b388043a