Schedule artifact expiry backfill again

What does this MR do?

After the previous rescheduling (!55093 (merged)), there was ~400.000 records left that still didn't get an expiry date. This reschedules the same background migration to cover the records that were left out.

Related https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/10177

Does this MR meet the acceptance criteria?

Conformity

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