ci(docker): build multi-arch images (amd64 + arm64)

[DavertMik]

Summary

Closes #5646 — the Docker Hub image (codeceptjs/codeceptjs) currently ships amd64 only. This PR makes the published image multi-arch so it works natively on ARM64 (Apple Silicon, AWS Graviton, Raspberry Pi, etc.).

Changes

• .github/workflows/docker.yml
  • Add docker/setup-qemu-action@v3 to enable arm64 emulation during the build.
  • Pass platforms: linux/amd64,linux/arm64 to build-push-action, producing a single multi-arch manifest. docker pull codeceptjs/codeceptjs then resolves to the right architecture automatically.
• Dockerfile
  • Bump base image mcr.microsoft.com/playwright:v1.55.0-noble → v1.61.0-noble (latest). This release ships an arm64 manifest and matches the project's playwright ^1.59.0 dependency, so the image's bundled browsers line up with the installed package.

Why this is sufficient

• Base image v1.61.0-noble publishes both amd64 and arm64 manifests (verified via docker manifest inspect).
• The Dockerfile has no arch-specific downloads; the apt packages (libgtk2.0-0, libxtst6, xvfb, …) exist for both arches on Ubuntu Noble.
• docker/entrypoint and docker/run.sh are plain shell, architecture-agnostic.

Notes / tradeoffs

• The arm64 image is built via QEMU emulation, which is slower (the npm install step in particular). If build time becomes a problem, a follow-up could split the build across native runners (ubuntu-22.04 + ubuntu-22.04-arm) and merge manifests with docker buildx imagetools.
• The base image is pinned to an exact version, so it won't drift — it should be bumped alongside future Playwright upgrades.

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