Finalize migration BackfillSubscriptionUserAddOnAssignmentsOrganizationId

What does this MR do and why?

This migration was finished, you can confirm the status using our batched background migration chatops commands.

To confirm it is finished you can run:

/chatops run batched_background_migrations status 1000659

The last time this background migration was triggered was in db/post_migrate/20240826120429_queue_backfill_subscription_user_add_on_assignments_organization_id.rb

You can read more about the process for finalizing batched background migrations in https://docs.gitlab.com/ee/development/database/batched_background_migrations.html.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.