Update get-started-with-viva-topics.md

[techtocore]

Fix documentation title to be consistent with the updated branding guidelines.

[learn-build-service-prod]

Learn Build status updates of commit c89bba5:

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microsoft-365/topics/get-started-with-viva-topics.md	✅Succeeded

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[v-jmathew]

Closing, since the page no longer exists as Viva Topics has been retired as of February 22, 2025.
Credit: https://learn.microsoft.com/en-us/microsoft-365/topics/changes-coming-to-topics?view=o365-worldwide