Bump golang in /integration/cloudbuild/testbase (#3217)

Bumps golang from `c870468` to `52362e2`.

---
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:c870468ff84060d43d719ed273d79c63d5fc2fa7a519744d0f25db29ca6b21ff
+FROM golang:1.21.4-bookworm@sha256:52362e252f452df17c24131b021bf2ebf1c9869f65c28f88ddb326191defea9c
 
 WORKDIR /testbase