[FIX][14.0] auth_saml: Add FOR UPDATE NOWAIT clause to SAML provider query

[Ricardoalso]

• Enhance concurrency handling when fetching SAML provider data
• Prevent potential deadlocks by using NOWAIT
• Ensure data consistency during high-traffic scenarios

Previous attempt using the locking mechanisms

self.env.cr.execute(
    "SELECT id FROM auth_saml_provider WHERE id in %s FOR UPDATE",
    (tuple(provider_ids),),
 )

led to increased latency and deadlocks under high load.

We experienced race conditions where two simultaneous login
attempts triggered parallel updates of the idp_metadata, leading to unreleased locks.

The FOR UPDATE NOWAIT clause addresses this issue by:

1. Acquiring an exclusive lock on the row being updated
2. Failing fast if the lock cannot be acquired (NOWAIT)
3. Ensuring that only one transaction can update the idp_metadata at a time

[gurneyalex]

Can you update the commit message:

• mention the other attempts with the locks, and the issues they caused
• explain the race condition we checked together this morning with 2 login attempts that will cause 2 updates of the idp_metadata in parallel
• explain how the fix is preventing this