Explicitly set the target platform of Docker builds

[nyanmisaka]

Recently an error popped up when I was building an arm64 image on amd64:

#4 [internal] load metadata for docker.io/arm64v8/debian:bookworm-slim
#4 ERROR: no match for platform in manifest: not found

#3 [internal] load metadata for docker.io/library/node:20-alpine
#3 CANCELED

#5 [internal] load metadata for docker.io/multiarch/qemu-user-static:x86_64-aarch64
#5 CANCELED
------
 > [internal] load metadata for docker.io/arm64v8/debian:bookworm-slim:
------
Dockerfile:91
--------------------
  89 |     #
  90 |     FROM multiarch/qemu-user-static:x86_64-${QEMU_ARCH} as qemu
  91 | >>> FROM ${IMAGE_ARCH}/debian:${OS_VERSION}-slim as combined
  92 |
  93 |     ARG OS_VERSION
--------------------
ERROR: failed to solve: arm64v8/debian:bookworm-slim: failed to resolve source metadata for docker.io/arm64v8/debian:bookworm-slim: no match for platform in manifest: not found

uraimo/run-on-arch-action#155
docker-library/python#933 (comment)

We've been slowly moving Official Images to a new build process and moved python yesterday, so now the arch-specific namespaces are an image index because they include attached provenance/sbom metedata.

It was caused by some upstream changes, where now the FROM directive requires you to explicitly set the platform type for multi-arch builds.

https://docs.docker.com/reference/dockerfile/#from

The optional --platform flag can be used to specify the platform of the image in case FROM references a multi-platform image. For example, linux/amd64, linux/arm64, or windows/amd64. By default, the target platform of the build request is used.

Their documentation is also out of date and does not reflect this new behavior.