fix mypy type errors in test_variable.py (apache#56802)

* fix mypy type errors in test_variable.py

* fix for static check

Author: rich7420

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

@@ -33,8 +33,9 @@
 from tests_common.test_utils.config import conf_vars
 
 if TYPE_CHECKING:
+    from sqlalchemy.orm import Session
+
     from airflow.models.team import Team
-    from airflow.settings import Session
 
 pytestmark = pytest.mark.db_test