PG19: enable PG19beta1 test matrices in CI

[ihalatci]

Turns on the PG19beta1 columns across the downstream Build & Test
matrices now that the build job already proves PG19 compiles under
-Werror and the ruleutils port (#8602) lands the runtime/regress
fixes those suites depend on.

Changes (.github/workflows/build_and_test.yml)

• test-citus, test-citus-failure, test-citus-cdc: add
  pg19_version to the pg_versions array.
• test-arbitrary-configs: add pg19_version to matrix.pg_version.
• test-pg-upgrade: add the 18 -> 19 and 16 -> 19 upgrade pairs
  (adjacent + oldest -> newest, consistent with the existing
  16->17 / 17->18 / 16->18 set).
• params: bump pg19_version / upgrade_pg_versions from 19devel
  to 19beta1, and point image_suffix at the PG19beta1-enabled
  the-process images (-dev-33b3cf5, built from
  Add PG19 (19beta1) and bump PG minors via apt the-process#222).

Deliberately not changed

• test-citus-upgrade stays at PG16/PG17 — no released Citus binary
  supports PG19, so there is nothing to upgrade from.

Dependencies

• Image set: Add PG19 (19beta1) and bump PG minors via apt the-process#222 (PG19beta1 via apt) — green,
  images published under -dev-33b3cf5.
• Runtime/regress fixes: ruleutils port PG19: port ruleutils into Citus as ruleutils_19.c #8602 plus the
  runtime/regress sub-issues must be on pg19-support for the new
  cells to pass.

Closes #8615
Part of #8597

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (pg19-support@34fb255). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff               @@
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  Hits                    ?    57161           
  Misses                  ?     4872           
  Partials                ?     2331           

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