You are explictly requesting the bookworm versions, I'm not sure what you're expecting?

At least google's got you covered, if you simply ask nicely:

  $ curl -s https://packages.cloud.google.com/apt/dists/cloud-sdk-trixie/InRelease | grep -E Suite:\|Date:
  Suite: cloud-sdk-trixie
  Date: Wed, 27 Aug 2025 18:45:14 UTC
  $ curl -s https://packages.cloud.google.com/apt/dists/google-compute-engine-trixie-stable | grep -E Suite:\|Date:
  Suite: google-compute-engine-trixie-stable
  Date: Mon, 25 Aug 2025 21:24:03 UTC