Update RichSuggestBox.md

[deltoro05]

This URL https://unicode-table.com/ has changed to https://symbl.cc/

[learn-build-service-prod]

Learn Build status updates of commit 1fb8a17:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/controls/RichSuggestBox.md	✅Succeeded	View

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[Arlodotexe]

This repo is for the 7.x version of the toolkit. This document can now be found in the source code for the RichTextBlock samples, which is deployed by tooling to this document for display on Microsoft learn.