ci: switch Go steps to gobuilder with S3-backed build cache

Use the estate gobuilder image for the Go test and pre-commit steps
and enable the shared GOCACHEPROG S3 cache to speed up CI builds.

.woodpecker/pre-commit.yaml

@@ -3,7 +3,7 @@ when:
 
 steps:
   - name: pre-commit
-    image: golang:1.25
+    image: artifactapi.k8s.syd1.au.unkin.net/docker-internal/gobuilder:0.1.2-alma9
     backend_options:
       kubernetes:
         serviceAccountName: kea-operator-ci
@@ -14,6 +14,18 @@ steps:
           limits:
             memory: 2Gi
             cpu: "2"
+    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-kea-operator
+      GOCACHE_METRICS: "true"
+      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
     commands:
       - test -z "$(gofmt -l .)"
       - go vet ./...

.woodpecker/test.yaml

@@ -3,7 +3,7 @@ when:
 
 steps:
   - name: test
-    image: golang:1.25
+    image: artifactapi.k8s.syd1.au.unkin.net/docker-internal/gobuilder:0.1.2-alma9
     backend_options:
       kubernetes:
         serviceAccountName: kea-operator-ci
@@ -14,5 +14,17 @@ steps:
           limits:
             memory: 2Gi
             cpu: "2"
+    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-kea-operator
+      GOCACHE_METRICS: "true"
+      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
     commands:
       - go test -race -count=1 ./api/... ./internal/...