0.1.2-alma9 left $GOPATH/bin off PATH, so release.yaml's goreleaser
step would have exited 127 after `go install` on the next tag.
0.1.3-alma9 sets GOPATH=/go and PATH=/go/bin:$PATH.
Switches the estate's older base images off in favor of the
shared gobuilder image and wires up the S3-backed Go build cache.
- Point build/test/lint-adjacent test/pre-commit/integration/release
steps at artifactapi.k8s.syd1.au.unkin.net/docker-internal/gobuilder:0.1.2-alma9
- Add GOCACHE_S3_* env and GOCACHEPROG=go-cache-plugin with an
absolute --cache-dir to each Go-toolchain step
- Leave the dedicated golangci-lint step and the RPM upload step
on their existing images