Fix: Add session rollback to FAB find_user on error to prevent invali…

[MonsterChenzhuo]

Description

This PR adds exception handling and session rollback to the find_user method in FabAirflowSecurityManagerOverride.

Motivation and Context

Currently, the find_user method in the FAB security manager override only catches MultipleResultsFound exceptions. If any other exception occurs during the database query (e.g., a temporary database disconnection, query timeout, or an _invalid_transaction state), the session is not rolled back.

This leaves the SQLAlchemy session in a broken/dirty state. Since sessions are often reused in the worker process, subsequent requests (like login attempts) fail continuously with errors like:

[boring-cyborg]

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[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.