fix: update postgres volume mount for Postgres 18+ compatibility

Changed volume mount from /var/lib/postgresql/data to /var/lib/postgresql
to match the new directory structure in Postgres 18+.

This fixes the error:
  'these Docker images are configured to store database data in a format
  which is compatible with pg_ctlcluster'

See: docker-library/postgres#1259

Author: claude

docker-compose.test.yaml

@@ -17,7 +17,7 @@ services:
       retries: 10
       start_period: 10s
     volumes:
-      - postgres-test-data:/var/lib/postgresql/data
+      - postgres-test-data:/var/lib/postgresql
 
   clickhouse-test:
     image: clickhouse/clickhouse-server:latest