When the PGDG repo is unreachable for trixie/forky/sid, the previous
code fell back to bookworm-pgdg. This causes unresolvable dependency
errors because bookworm-pgdg packages depend on libldap-2.5-0 and
libicu72, which don't exist on Trixie (has libldap-2.6-0 and libicu76).
Instead of falling back to an incompatible suite, recursively call
setup_postgresql with USE_PGDG_REPO=false to use Debian's native
PostgreSQL packages (Trixie ships PG 17 natively).