ci(postgres): fail setup if pg_ctl stop fails before baking the datadir

The "Stop DB and stage datadir" step swallowed a failed `pg_ctl -m fast -w
stop` with `|| true`, then moved and tarred the PGDATA regardless. A stop
that times out or errors would bake a still-running, crash-inconsistent
cluster into the artifact every test shard consumes — and with
full_page_writes off, crash recovery can't repair torn pages. Drop the
`|| true` so a failed stop fails the job, mirroring the MariaDB sister's
"don't bake a dirty datadir" guard.

Also drop the redundant `ALTER SYSTEM SET fsync/synchronous_commit/
full_page_writes = off` block from install.sh. Its comment claimed the
postgres workflow "runs a service-container DB and never calls start-db.sh",
but it does call start-db.sh, which already applies those flags via `-o` on
every postgres start (setup job and each shard). The block was a no-op and
its justification was factually wrong.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/helper/install.sh

@@ -297,14 +297,10 @@ if [ "$DB" == "postgres" ];then
     echo "travis" | psql -h 127.0.0.1 -p 5432 -c "CREATE DATABASE test_frappe" -U postgres;
     echo "travis" | psql -h 127.0.0.1 -p 5432 -c "CREATE USER test_frappe WITH PASSWORD 'test_frappe'" -U postgres;
 
-    # Disposable CI DB: durability off for speed (postgres fsyncs every commit by default, which
-    # dominates a commit-heavy suite). All reloadable, no restart. The postgres workflow runs a
-    # service-container DB and never calls start-db.sh, so the flags must be applied here.
-    echo "travis" | psql -h 127.0.0.1 -p 5432 -U postgres \
-        -c "ALTER SYSTEM SET synchronous_commit = 'off'" \
-        -c "ALTER SYSTEM SET fsync = 'off'" \
-        -c "ALTER SYSTEM SET full_page_writes = 'off'" \
-        -c "SELECT pg_reload_conf()";
+    # Durability-off for speed (no fsync/synchronous_commit/full_page_writes) is applied by
+    # start-db.sh's postgres `-o` flags on every start — setup job AND each test shard — so it is
+    # NOT repeated here. The postgres workflow runs in-runner via start-db.sh, not a service
+    # container.
 fi
 
 cd ~/frappe-bench || exit