Update to Update-ClusterFunctionalLevel

[Xelu86]

PR Summary

Updating language per PM/Dev as cmdlet already states it supports WS12 R2 and above for VM node upgrades.

PR Checklist

• Descriptive Title: This PR's title is a synopsis of the changes it proposes.
• Summary: This PR's summary describes the scope and intent of the change.
• Contributor's Guide: I have read the contributors guide.
• Style: This PR adheres to the style guide.

[learn-build-service-prod]

Learn Build status updates of commit 1312b2b:

✅ Validation status: passed

File	Status	Preview URL	Details
docset/winserver2025-ps/FailoverClusters/Update-ClusterFunctionalLevel.md	✅Succeeded	View (WindowsServer2025-ps)

For more details, please refer to the build report.