Correct the Session argument's type hint in ApplessSecurityManager (#…

…44962)

In #33901 this was moved to a new file and mistakenly changed to
flask_session.

It's not clear to me why this didn't cause errors, but it was highlighted in
my editor as an invalid type 🤷

airflow/www/security_appless.py

@@ -21,7 +21,7 @@
 from airflow.providers.fab.auth_manager.security_manager.override import FabAirflowSecurityManagerOverride
 
 if TYPE_CHECKING:
-    from flask_session import Session
+    from sqlalchemy.orm import Session
 
 
 class FakeAppBuilder: