fix: wait for title before updating announcer

[geoffrich]

Fixes #10360

When you set the page title using $page.data in a layout (see linked issue for the concrete use case), the document's title is not updated until after the page store has fired its subscription callbacks. This means that the announcer uses the previous page's title instead and announces the wrong route.

This PR fixes this by waiting a tick before reading the new title.

No test, because the existing ones set the title directly in each page component, and refactoring those to return the page title instead seemed like too much for an edge case.

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