There's a closed pull request on the void-packages repository

gtk4: move IconBrowser4 into gtk4-demo
https://github.com/void-linux/void-packages/pull/37881

Description:
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#### Testing the changes
- I tested the changes in this PR: **YES**

This moves the icon browser demo into `gtk4-demo`.
It isn't really that big of a deal, but it bothers people.

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