fix: resolve ruff linter errors in psycopg system tests

Author: kgala2

tests/system/test_psycopg_connection.py

@@ -13,11 +13,11 @@
 See the License for the specific language governing permissions and
 limitations under the License.
 """
+from __future__ import annotations
 
 import asyncio
 from datetime import datetime
 import os
-from typing import Union
 
 import pytest
 import sqlalchemy
@@ -34,7 +34,7 @@ def create_sqlalchemy_engine(
     db: str,
     ip_type: str = "public",
     refresh_strategy: str = "background",
-    resolver: Union[type[DefaultResolver], type[DnsResolver]] = DefaultResolver,
+    resolver: type[DefaultResolver | DnsResolver] = DefaultResolver,
 ) -> tuple[sqlalchemy.engine.Engine, Connector]:
     """Creates a connection pool for a Cloud SQL instance and returns the pool
     and the connector.