Chore: Update docker to 29.1.2

The current image is too old, doesn't support modern Dockerfile syntax, so downstream projects have to resort to using docker file syntax override, which in turn creates roundtrip to docker.io, which is known to hit rate limits.

RUN \
<<eot sh -eux
  # Use sane permissions until solved upstream
  # https://gitlab.com/gitlab-org/gitlab-runner/-/issues/1736
  chmod -R a+rX,og-w .
eot

$ docker build .
[snip]
ERROR: failed to solve: rpc error: code = Unknown desc = failed to solve with frontend dockerfile.v0: failed to create LLB definition: dockerfile parse error line 27: unknown instruction