fix mypy type errors in test_pool.py (apache#56801)

Co-authored-by: Shahar Epstein <60007259+shahar1@users.noreply.github.com>

Author: rich7420

airflow-core/tests/unit/models/test_pool.py

@@ -19,10 +19,10 @@
 
 from typing import TYPE_CHECKING
 
+import pendulum
 import pytest
 
 from airflow import settings
-from airflow._shared.timezones import timezone
 from airflow.exceptions import AirflowException, PoolNotFound
 from airflow.models.dag_version import DagVersion
 from airflow.models.pool import Pool
@@ -39,12 +39,13 @@
 )
 
 if TYPE_CHECKING:
+    from sqlalchemy.orm import Session
+
     from airflow.models.team import Team
-    from airflow.settings import Session
 
 pytestmark = pytest.mark.db_test
 
-DEFAULT_DATE = timezone.datetime(2016, 1, 1)
+DEFAULT_DATE = pendulum.datetime(2016, 1, 1, tz="UTC")
 
 
 class TestPool: