Two release-workflow fixes uncovered while trying to ship 0.7.10:
1. mount-s3.deb hardcodes the x86_64 binary path. Building for
linux/arm64 in parallel fired the dpkg "wrong architecture" error
under qemu. Daytona sandboxes are x86_64-only anyway, so drop arm64.
If we ever need arm64 (Mac silicon dev, alt providers), switch the
Dockerfile to TARGETARCH-aware URLs.
2. docker job depended on [test] alongside publish, so the two ran in
parallel. The Dockerfile installs polpo-ai@${VERSION} from npm,
which intermittently isn't published yet when docker reaches that
step. Make docker [needs: publish] so the install always finds the
package.