Remove subtransaction in Security::ProcessScanResultPolicyWorker

What does this MR do and why?

Addresses #396743 (closed)

This MR removes the usage of safe_find_or_create_by! for SoftwareLicense when it is created through License approval policies as it creates a subtransaction from Security::ProcessScanResultPolicyWorker. We don't need to do it in a transaction as we already have exclusive leave on the worker so there won't be a race condition.

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