Fix permissions on :read_pipeline_schedule ability

What does this MR do and why?

Currently, a public user is able to view the /pipeline_schedules page in a public project that has "Public pipelines" disabled. Per documentation, CI/CD menu items (which includes "Pipeline schedules") should not be publicly visible when "Public pipelines" is disabled.

This MR fixes the :read_pipeline_schedule ability to correct the visibility behaviour.

Resolves: #416643 (closed)

How to reproduce

1. As the admin of a public Project, create any Scheduled pipeline at /<group>/<project>/-/pipeline_schedules.
2. In your Project CI/CD settings, uncheck the Public pipelines setting and click Save changes.

3. As an unauthenticated user (I recommend opening a new browser window with a different session), go to /<group>/<project>/-/pipeline_schedules and observe that the page content is visible.

How to set up and validate locally

1. Follow Steps 1-2 in the above section.
2. As an unauthenticated user, go to /<group>/<project>/-/pipeline_schedules and observe that the page now returns a 404 error.

3. Just for safe measure, check that your project admin user still has access to that page.
4. Enable Public pipelines in your Project's CI/CD settings and confirm that /<group>/<project>/-/pipeline_schedules is now visible for both the authenticated and unauthenticated user.

MR acceptance checklist

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