Upgrade `sidekiq-cron` gem

Follow up from Ruby 3.3/3.4 Gem compatibility reviews gitlab-org/gitlab#541453 (comment 2659551680)

This issue is to track the upgrade from sidekiq-cron 1.12.0 to the latest version 2.3.0 (https://github.com/sidekiq-cron/sidekiq-cron/blob/v2.3.0/.github/workflows/ci.yml#L15) to ensure Ruby 3.3/3.4 compatibilities.

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Upgrade sidekiq-cron gem