Use content_id for matching list items

[unoduetre]

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What

Use content_id instead of base_path for matching list items. This fixes the following bug. A video showing the bug is attached to the Trello card.

Reported by Polly Green in the Yellow team https://gds.slack.com/archives/CACV3TACU/p1689250423550889 and I’ve just tested the following on integration:

1. Go to a curated section of mainstream browse, for example
   https://www.integration.publishing.service.gov.uk/browse/childcare-parenting/schools-education
2. Choose one content page in the list and change the slug for it
3. Publish the slug change for the content item
4. Check browse page and content item with the new slug still appears in the list.
5. I then removed another page from the same list, under the same subheading as the content item that had the slug change. Removing the other content item, also removes the content item that had the slug changed.
6. But the content item that had the slug change still appears in collections publisher under the same heading, but does not show on the front end anymore.

Why

Trello ticket

Dependencies

This PR depends on merging #2223 first and applying the rake task.