Switch Go CI steps to gobuilder + S3 build cache

Cuts go vet/go test wall time via a shared package-object cache.

- pre-commit and test steps move from docker.io/golang:1.26 to the
  pinned estate gobuilder image (go1.26.7, trusts the internal CA)
- wire GOCACHEPROG to go-cache-plugin against the S3 cache bucket,
  creds from org-level GOCACHE_AWS_* secrets
- bump test step memory limit to 4Gi for envtest + -race headroom
- buildx steps (build.yaml, docker.yaml) untouched: compilation
  happens inside Dockerfile.operator, not the Woodpecker step

.woodpecker/pre-commit.yaml

@@ -3,10 +3,21 @@ when:
 
 steps:
   - name: pre-commit
-    image: golang:1.26
+    image: artifactapi.k8s.syd1.au.unkin.net/docker-internal/gobuilder:0.1.2-alma9
     commands:
       - test -z "$(gofmt -l cmd/ internal/)"
       - go vet -mod=vendor ./...
+    environment:
+      GOCACHE_S3_BUCKET: gocache
+      GOCACHE_S3_REGION: us-east-1
+      GOCACHE_S3_ENDPOINT_URL: "https://s3.ceph.unkin.net"
+      GOCACHE_S3_PATH_STYLE: "true"
+      GOCACHE_KEY_PREFIX: ci-autobackup-operator
+      GOCACHEPROG: "go-cache-plugin --cache-dir=/tmp/gocache"
+      AWS_ACCESS_KEY_ID:
+        from_secret: GOCACHE_AWS_ACCESS_KEY_ID
+      AWS_SECRET_ACCESS_KEY:
+        from_secret: GOCACHE_AWS_SECRET_ACCESS_KEY
     backend_options:
       kubernetes:
         serviceAccountName: autobackup-operator-ci

.woodpecker/test.yaml

@@ -3,12 +3,23 @@ when:
 
 steps:
   - name: test
-    image: golang:1.26
+    image: artifactapi.k8s.syd1.au.unkin.net/docker-internal/gobuilder:0.1.2-alma9
     commands:
       # Fetch the envtest control-plane binaries; the controller tests skip
       # gracefully if this cannot be downloaded.
       - export KUBEBUILDER_ASSETS="$(go run sigs.k8s.io/controller-runtime/tools/setup-envtest@latest use 1.31.0 -p path 2>/dev/null)"
       - go test -race -count=1 -mod=vendor ./...
+    environment:
+      GOCACHE_S3_BUCKET: gocache
+      GOCACHE_S3_REGION: us-east-1
+      GOCACHE_S3_ENDPOINT_URL: "https://s3.ceph.unkin.net"
+      GOCACHE_S3_PATH_STYLE: "true"
+      GOCACHE_KEY_PREFIX: ci-autobackup-operator
+      GOCACHEPROG: "go-cache-plugin --cache-dir=/tmp/gocache"
+      AWS_ACCESS_KEY_ID:
+        from_secret: GOCACHE_AWS_ACCESS_KEY_ID
+      AWS_SECRET_ACCESS_KEY:
+        from_secret: GOCACHE_AWS_SECRET_ACCESS_KEY
     backend_options:
       kubernetes:
         serviceAccountName: autobackup-operator-ci
@@ -17,5 +28,5 @@ steps:
             memory: 1Gi
             cpu: 1
           limits:
-            memory: 2Gi
+            memory: 4Gi
             cpu: 2