Bump golang in /integration/cloudbuild/testbase (#3346)

Bumps golang from 1.21.6-bookworm to 1.22.0-bookworm.

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

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

Author: dependabot[bot]

integration/cloudbuild/testbase/Dockerfile

@@ -1,5 +1,5 @@
 # This Dockerfile builds a base image for Trillan integration tests.
-FROM golang:1.21.6-bookworm@sha256:3efef61ff1d99c8a90845100e2a7e934b4a5d11b639075dc605ff53c141044fc
+FROM golang:1.22.0-bookworm@sha256:874c2677e43be36a429823f2742af85844772664f273c1c8c8235f10aba51cd3
 
 WORKDIR /testbase