fix(header): use aria attributes to hide small title when collapsed (#30027)

Issue number: resolves #29347 

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## What is the current behavior?
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Focusable elements like buttons cannot be accessed within the
`ion-header` when it's collapsed. They're only accessible once the small
title is displayed.

## What is the new behavior?
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this PR. -->

- Moved the `aria-hidden` from the header to `ion-title`, this aligns
with native.
- Updated existing test.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->

Dev build: `8.4.1-dev.11732064156.12837790`