Update set-up-admin-center.md

[JarbasHorst]

Edits based on the Microsoft Writing Style Guide.

[learn-build-service-prod]

Learn Build status updates of commit 59514d8:

✅ Validation status: passed

File	Status	Preview URL	Details
Viva/connections/set-up-admin-center.md	✅Succeeded

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[learn-build-service-prod]

Learn Build status updates of commit 7c3d81a:

✅ Validation status: passed

File	Status	Preview URL	Details
Viva/connections/set-up-admin-center.md	✅Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[scanum]

@AtkinE
PR has been copyedited and is ready for final review, could you please check and merge? Thanks!