Navigation overlay: update area description

[t-hamano]

Trac ticket: https://core.trac.wordpress.org/ticket/64589

Use of AI Tools

No AI tools were used in this PR.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

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Props wildworks, scruffian.

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[scruffian]

Good changes, thanks.

[github-actions]

Test using WordPress Playground

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Test this pull request with WordPress Playground.

[t-hamano]

This PR was committed in [61734]