Fix pipeline schedule table for missing owner

What does this MR do and why?

Fix pipeline schedule table for missing owner

When a pipeline schedule has not owner, there is a missing reference in the pipelines schedules template.

References

• https://gitlab.com/gitlab-org/gitlab/-/issues/583152#note_2939061896

Screenshots or screen recordings

How to set up and validate locally

To reproduce locally, visit the pipeline schedules e.g. /my-group/my-project/-/pipeline_schedules/ create a schedule. Then remove its owner, in rails c

Ci::PipelineSchedule.last.update!(owner_id: nil)

Visit the page and ensure there are no errors in the console.

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Related to #583152