Update modern-root-site.md

[calebmil]

Added warning to run Page Diagnostics before attempting root site swap. Aligns doc with the documentation for the same function in PowerShell.

[learn-build-service-prod]

Learn Build status updates of commit 4384664:

💡 Validation status: suggestions

File	Status	Preview URL	Details
SharePoint/SharePointOnline/modern-root-site.md	💡Suggestion		Details

SharePoint/SharePointOnline/modern-root-site.md

• Line 100, Column 75: [Suggestion: preserve-view-not-set - See documentation] You've pinned this link to a specific version of content with the view parameter. It's recommended not to pin a version unless that version is A) not the default view and B) the context is about that version specifically. To proceed with pinning a version add the &preserve-view=true to the URL. Otherwise, remove the view parameter. URL: /microsoft-365/enterprise/page-diagnostics-for-spo?view=o365-worldwide

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[learn-build-service-prod]

Learn Build status updates of commit 6af9a58:

✅ Validation status: passed

File	Status	Preview URL	Details
SharePoint/SharePointOnline/modern-root-site.md	✅Succeeded

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