Fix: Remove the scrollbar issue when image lightbox is active

[Sourav61]

Fixed the image lightbox scrollbar issue when image lightbox is active

What?

Closes #69527

Why?

When the image lightbox is opened, the scrollbar is available even though there is no content to be displayed other than the image.

How?

• Added appropriate css to remove the scrollbar when the image lightbox is active

Testing Instructions

1. Add an Image block in the editor.
2. In the block toolbar, open Link settings and enable the Enlarge on Click option.
3. Preview the page and click on the image to open the lightbox with the .zoom.active class.
4. Scroll the page and observe that the scrollbar remains visible instead of being hidden.

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Co-authored-by: Sourav61 <sourav08@git.wordpress.org>

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