Storybook: fading of page contents not working with multiple pages of StoryQuests

### Threadbare version

_No response_

### Affected scene

storybook.tscn

### Description

When more than 16 StoryQuests are available and you must go to the next page to access the rest, the fading in and out of the page contents doesn't work.

### Checklist

- [x] I've reviewed and agree to follow the code of conduct