chore(deps): update golang:1.25.4 docker digest to 6ca9eb0 (#1432)

Co-authored-by: elastic-renovate-prod[bot] <174716857+elastic-renovate-prod[bot]@users.noreply.github.com>

Author: elastic-renovate-prod[bot]

.buildkite/release.yml

@@ -1,7 +1,7 @@
 steps:
   - label: Release
     agents:
-      image: "golang:1.25.4@sha256:5d73b7b83dd6e0258ff62832c93b6ea208fbb7727985d265fb49f75f81fc3d1f"
+      image: "golang:1.25.4@sha256:6ca9eb0b32a4bd4e8c98a4a2edf2d7c96f3ea6db6eb4fc254eef6c067cf73bb4"
       cpu: "16"
       memory: "24G"
       ephemeralStorage: "20G"