Image Banner: set height explicitly to preserve scroll state in safari

[RasmusKjeldgaard]

Which issue does this PR close?

This PR closes #3810

What is the new behavior?

See issue for background.
Scroll state is now preserved because the image-banner has explicit height set.

Does this PR introduce a breaking change?

• Yes
• No

Are there any additional context?

Checklist:

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Reminders

• Make sure you have implemented tests following the guidelines in: "The good: Test".
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Review

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When the pull request has been approved it will be merged to develop by Team Kirby.