Pass arch value to --platform

[LecrisUT]

This comes from a debugging session in #152. It seems to resolve issues like:

  Dockerfile.s390x.ubuntu18.04:1
  --------------------
     1 | >>> FROM s390x/fedora:latest
     2 |     COPY ./run-on-arch-install.sh /root/run-on-arch-install.sh
     3 |     RUN chmod +x /root/run-on-arch-install.sh && /root/run-on-arch-install.sh
  --------------------
  ERROR: failed to solve: s390x/fedora:latest: failed to resolve source metadata for docker.io/s390x/fedora:latest: no match for platform in manifest: not found

[martin-g]

Suggested change

	unset ARCH
	export ARCH=amd64

[LecrisUT]

I was thinking if we should allow an interface to not pass --platform, that was the reason for unset approach

[martin-g]

Suggested change

	${ARCH:+--platform=linux/$ARCH} \
	--platform=linux/$ARCH \

[martin-g]

Suggested change

	${ARCH:+--platform=linux/$ARCH} \
	--platform=linux/$ARCH \

[LecrisUT]

One other thing I should ask. I was able to debug locally with podman and I got much further than with this action. I suspect it's because this needs to be passed to docker run as well?

Edit: I've tried adding it to docker run as well, but that didn't help, still the same error: maciejhirsz/logos#428. Running locally with podman works just fine 🤷

[martin-g]

Probably it will be a good idea to start using buildx instead