Swap golang:1.25 and almalinux9-gobuilder:20260606 to the estate
gobuilder image on every step invoking the Go toolchain (build, test,
pre-commit, release test/build). Add GOCACHE_S3_* env and GOCACHEPROG
pointing go-cache-plugin at an absolute /tmp/gocache cache dir, backed
by the shared S3 bucket via org secrets.