docker release: build per-platform on native runners, drop mode=max cache
The build job built every platform of a variant on one runner, so 2-4 Go
cross-compiles fought over a single 2-vCPU box and arm64 ran in an emulated
context. Split the matrix to one platform per job on a native runner
(amd64/386 on ubuntu-latest, arm64/arm-v7 on ubuntu-24.04-arm); only arm/v7
still needs QEMU, and only for its final apk stage. Each job pushes by
digest, and a new merge job assembles the multi-arch tag with imagetools
and mirrors it to Docker Hub.
cache-to mode=max -> mode=min: BRANCH=sha cache-busts the heavy go-build
layer every release, so writing all intermediate layers to the gha backend
spent 3-11 min per variant on a cache the next release's sha can never hit.
Chris LuandGitHub
3f68b19500