Nightly arm64 failures (2026-09-12)

Nightly arm64 run failed.

Run: https://github.com/citusdata/citus/actions/runs/34672310562

Failing jobs:
- arm64 PG17 - regress
- arm64 PG18 - regress

New failures not previously tracked:
- arm64 PG17 - regress

This is the phase-1 arm64 gate (assert-off): a failure here means Citus did not
build or pass core regression/isolation tests natively on arm64.

Start with the linked GitHub Actions run 34672310562 and inspect the logs for the arm64 PG17 and PG18 regress jobs, paying particular attention to the new PG17 failure. Compare the results with previously tracked arm64 failures; done means the cause is identified and the phase-1 arm64 regression gate passes again.

Written by the indexing model from the issue text.