Finalize EncryptMissedRunnerTokens

In this MR (maintenance: Encrypt missed ci_runner plain tokens (!196265 - merged)), we have queued a bbm which we have to finalise in %18.3 . Enqueued in %18.2

References: #410315 (closed) https://docs.gitlab.com/development/database/batched_background_migrations/#finalize-a-batched-background-migration