Update Go to 1.27.3

Vishal Takrequested to merge
vtak/go-1.27.3 into main

What does this MR do?

  • Updates Go to 1.27.3, from 1.27.2, in the build image (Dockerfile) and the CI image (.gitlab/ci/Dockerfile), and points CI_IMAGE at ci:go1.27.3-alpine. Changing .gitlab/ci/Dockerfile makes the prepare stage build and push that CI image in this MR's pipeline.
  • Starts the v0.16.2-gitlab.64 release in CHANGELOG.md and sets version/version.go to match. v0.16.2-gitlab.63 is already tagged, so the default branch's daily scheduled pipeline releases v0.16.2-gitlab.64 once this merges, or run release from changelog by hand to release sooner.

Why was this MR needed?

Go 1.27.3 (released 2026-10-19) includes security fixes to the crypto/x509 package. See https://go.dev/doc/devel/release#go1.27.3.

base-images follows docker-machine releases, so the runner images pick up v0.16.2-gitlab.64 through Renovate there.

What's the best way to test this MR?

A green pipeline: the binaries build with golang:1.27.3, and release check accepts the new section and its matching Version.

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