Update four eyes policy threshold

PUT https://sandbox.depasify.com/api/v1/four_eyes_policies/{id}

Updates the threshold of an existing four eyes policy.
This endpoint allows modification of the threshold_eur parameter for a policy. The threshold determines the minimum amount (in EUR) that triggers the four eyes approval requirement.
Important: The four eyes principle is designed for environments with multiple users, typically when the API is accessed through a frontend application. If you are using the API directly with an API key, alternative approaches for managing payment approvals may need to be evaluated, as the standard four eyes workflow requires two separate users.