Bump golang in /integration/cloudbuild/testbase (#3197)

Bumps golang from `932f877` to `85aacbe`.

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

integration/cloudbuild/testbase/Dockerfile

@@ -1,5 +1,5 @@
 # This Dockerfile builds a base image for Trillan integration tests.
-FROM golang:1.21.4-bookworm@sha256:932f877305d36da8a0b3a87bc60d278245a60ea2747c49a3c02da551ad57beb4
+FROM golang:1.21.4-bookworm@sha256:85aacbed94a248f792beb89198649ddbc730649054b397f8d689e9c4c4cceab7
 
 WORKDIR /testbase