build-package (all-pg-azure-storage): `citus/packaging:ubuntu-focal-all release` exits 1 silently after PG-version banner

## Symptom
On `migrate/all-pg-azure-storage-app-token`, the build-package "Build packages" step runs `docker run citus/packaging:ubuntu-focal-all release`, prints only its 3-line PostgreSQL-version banner, then exits 1 with NO inner build error and NO auth error. Publish is correctly skipped (branch ≠ MAIN_BRANCH).

## Evidence it is NOT the token migration and NOT the pin
- App-token steps GREEN in all runs (mint / export both GH_TOKEN+GITHUB_TOKEN / clone tools).
- **Pin EXONERATED:** run 28519513963 (SHA 45745bf) reverted the tools pin to the last-green `v0.8.28` and failed identically to the `v0.8.36` runs (28518692981, 28519998752).
- **Access CONFIRMED by owner:** `cituspackagingapp` has access to `citusdata/pgazure`.
- Same-day all-citus `v0.8.36` app-token build-package (28505518289) was fully GREEN.

## Classification
H1 — environmental drift of the mutable `citus/packaging:ubuntu-focal-all` image between the last green base run 27188719742 (2026-06-09, SHA e6d4079, unmigrated) and 2026-07-01. Base branch e6d4079 sat unmigrated and was NOT re-run in that window, so there is no same-period unmigrated control on this image.

## Suggested owner follow-up (not done here)
- Inspect the focal-all container's inner stderr (raw log zip).
- Compare the current `citus/packaging:ubuntu-focal-all` digest vs the 2026-06-09 build.
- And/or run a fully-unmigrated (`v0.8.28` + org PAT, app-token block removed) build-package from e6d4079 on a throwaway branch to definitively separate H1 from any residual token interaction (publish stays gated OFF on a non-MAIN branch).

## Related
Blocks merge of the GitHub App token migration PR #1192 (merge held pending resolution).

Start with the raw log zip for the Build packages step and inspect the focal-all container's inner stderr. Compare the current citus/packaging:ubuntu-focal-all digest with the 2026-06-09 build, then run the suggested unmigrated e6d4079 build using v0.8.28 and an org PAT. Done means the cause of the silent exit is separated between image drift and token interaction.

Written by the indexing model from the issue text.