Switch image matrices to PostgreSQL 17/18 and adopt tools v0.8.39

[ibrahim halatci (ihalatci)]

What

Activates the PostgreSQL 18 image, retires PostgreSQL 16, and moves every workflow onto tools v0.8.39.

This is phase 2 of 3 for PG19 support. Phase 1 (#383) added the image content; this phase wires it into the build matrices. Phase 3 is blocked externally (see below).

Change	Files
Matrices postgres_16 → postgres_18	publish_docker_images_{cron,on_push,on_tag}.yml
tools pin → v0.8.39	all 5 publish/update workflows
Drop postgres_16_version	pkgvars
Delete PG16 image	postgres-16/Dockerfile
Citus 14.1.0 → 14.2.0	postgres-18/Dockerfile

8 files, +10/−53.

Why the pin bump and the matrix change are one commit

v0.8.39 removes postgres_14, postgres_15 and postgres_16 from DockerImageType. Re-pinning while - postgres_16 is still in a matrix would hard-fail on an invalid enum value, and swapping the matrix without the pin would fail on an unknown postgres_18. They have to land together.

update_version.yml was still on v0.8.36; the other four were on v0.8.38.

Why postgres-18/Dockerfile also changes

pkgvars has carried postgres_18_version since February but the pg18 tag has never actually been published, so the file went stale — it was pinned to Citus 14.1.0 while master moved to 14.2.0. Publishing it as-is would ship pg18 with an older Citus than latest and pg17. All three corrected pins are verified published for PG18:

• postgresql-18-citus-14.2=14.2.0.citus-1
• postgresql-18-hll=2.21.citus-1
• postgresql-18-topn=2.7.1.citus-1

Why PostgreSQL 16 goes

Citus no longer supports it. It is also the cause of the currently failing nightly package builds, which die on citus/packaging:almalinux-8-pg16.

Why postgres_19 is not here

PostgreSQL 19 is still 19beta3 — there is no GA tag on Docker Hub — and no postgresql-19-citus package exists at any version. The image cannot build yet. postgres-19/Dockerfile stays in the tree unreferenced, and update_version.yml will refresh it on the next version bump now that the pin understands postgres19.

Phase 3 will add - postgres_19 to the matrices, flip the root and alpine Dockerfiles to PG19 GA, and re-pin off 19beta3.

Effect on merge

master is the only branch that publishes (publish_docker.py gates on it), so CI here is build-only. Once merged:

• pg18 is published for the first time
• pg16 stops being refreshed
• latest, alpine, pg17, nightly are unaffected

Note on publish_docker_images_on_manual.yml

That workflow passes no --image_type, so it builds every regular image. It is already broken on master: under v0.8.38 it tries to build postgres-14/ and postgres-15/, which don't exist in this repo. This PR improves it — every image it now resolves has a matching directory — though its main trigger will still fail on postgres_19 until Citus publishes PG19 packages. It's workflow_dispatch-only.

[ibrahim halatci (ihalatci)]

Follow-up phase 3 (PG19 GA) is tracked in #387 — blocked on PostgreSQL 19 going GA and Citus publishing PG19 packages.

Worth flagging one ordering constraint captured there: update_docker.py generates latest/alpine from postgres_19_version, which is still 19beta3 in pkgvars. That bump must land before update_version.yml is dispatched for the Citus 15 release, otherwise citus:latest gets pinned to a PG19 beta. Nothing in this PR triggers that — update_version.yml is workflow_dispatch only and the publish workflows just build the Dockerfiles as they already exist.