Fix RadioGroup component example in its readme

[DietPawel]

Description

I had to modify example to get it working, because components are exported with __experimental prefix.

How has this been tested?

n/a

Types of changes

Readme change

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.

[youknowriad]

Makes sense but since it's experimental, you should probably not use it as it can break in the future.

[github-actions]

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