Action fails because docker contains doesn't contains mksquashfs
You are probably already aware of this, but the action currently fail because the https://hub.docker.com/r/appimagecrafters/appimage-builder docker image doesn't include mksquashfs
The image should probably be updated to include it
Any way to fix this inside the action itself for the time bieng?
I have been trying to figure this one out but haven't had any luck myself. I don't know how to get that program to available inside the docker image for a workaround
You can run
apt-get update && apt-get install -y --no-install-recommends squashfs-tools
as part of your script section as a workaround for the time being.
The issue was fixed in the image by commit cf1a153, but there's no release yet.
Related upstream issue is https://github.com/AppImageCrafters/appimage-builder/issues/271