Improve SQLite test DB health checks

[henry3260]

Why

User can end up with a stale local SQLite test DB after migration squashes, reverts, or schema changes.
Before this change, pytest could skip DB initialization just because the marker file existed, even when the SQLite DB no longer matched the current Airflow metadata or migration heads.

That left contributors with confusing test failures and often required manually figuring out that the local SQLite DB needed to be removed or recreated.

closes : #44377

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[henry3260]

cc @potiuk I'd love to get your thoughts on this when you have a moment.