ci(postgres): warm up test data before baking the datadir

Mirror frappe/erpnext#56655 for the Postgres CI. Run the
bootstrap_test_data module in the setup job while Postgres is still up, so
the BootStrapTestData records are baked into the PGDATA artifact every shard
hydrates from — the shards start on already-warmed data instead of each
building it.

Unlike the MariaDB step, no `su -m` wrapper: the Postgres CI is
GitHub-hosted ubuntu-latest running as the runner user directly, matching
its own "Run Tests" step.

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

.github/workflows/server-tests-postgres.yml

@@ -105,6 +105,11 @@ jobs:
           FRAPPE_BRANCH: develop
           BENCH_CACHE_DIR: /home/runner/bench-cache
 
+      - name: Warm up test data
+        run: |
+          cd ~/frappe-bench/
+          bench --site test_site run-tests --lightmode --module erpnext.tests.bootstrap_test_data
+
       - name: Stop DB and stage datadir
         run: |
           PG_BIN=$(ls -d /usr/lib/postgresql/*/bin | sort -V | tail -1)