Block Pattern Previews appear broken for full-height cover blocks with a fixed background image

[kjellr]

When the parallax option is active on a full-height block pattern's cover block, the pattern preview only displays a portion of the image:

Preview:

Live Pattern:

To reproduce:

1. Add a block pattern that uses a full-height cover block with a fixed background.
2. View the pattern preview in the block inserter.

Sample:

<!-- wp:cover {"url":"https://cldup.com/7zTYWtDXdo.jpg","id":2653,"hasParallax":true,"minHeight":100,"minHeightUnit":"vh"} -->
<div class="wp-block-cover has-background-dim has-parallax" style="background-image:url(https://cldup.com/7zTYWtDXdo.jpg);min-height:100vh"><div class="wp-block-cover__inner-container"><!-- wp:paragraph {"align":"center","placeholder":"Write title…","fontSize":"large"} -->
<p class="has-text-align-center has-large-font-size">This is a cover block pattern.</p>
<!-- /wp:paragraph --></div></div>
<!-- /wp:cover -->