Add ApplicationContext to the Namespaces::PruneAggregationSchedulesWorker

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To make sure we have context for all of the workers (gitlab-com/gl-infra/scalability#131), please add context to the Namespaces::PruneAggregationSchedulesWorker since this schedules the Namespaces::RootStatisticsWorker.

Some more info in https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/development/sidekiq_style_guide.md#worker-context