LinkControl: Prevent space being reserved for scrollbar when items fit box

[frontdevde]

Description

This is a minor fix for a visual issue described in #19627 where the LinkControl search results box always reserves space for the scrollbar even when the results fit the box.

Please note that in order to test/observe the issue on master an external mouse must be connected.

Fixes #19627

How has this been tested?

• Connect an external mouse
• Add the navigation block
• Add a new link and find a search result that has three or less results
• Observe whether space for the scrollbar is reserved

Screenshots

Types of changes

Before:

After:

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR. .