e2e-gcloud(deps): bump golang in /images/e2e-gcloud

Bumps golang from 1.23.5-alpine3.21 to 1.23.6-alpine3.21.

---
updated-dependencies:
- dependency-name: golang
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

images/e2e-gcloud/Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.23.5-alpine3.21 as base
+FROM golang:1.23.6-alpine3.21 as base
 
 RUN set -eux; \
     apk upgrade --no-cache; \