powershell-style-guide.md: Update PlatyPS schema link

[SamB]

PR Summary

PlatyPS moved: https://github.com/PowerShell/platyPS/blob/master/platyPS.schema.md
to:
https://github.com/PowerShell/platyPS/blob/master/docs/developer/platyPS/platyPS.schema.md
so our link broke.

Fix it, tweak the link range, and use more descriptive link labels for the PlatyPS links.

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 fafc5cd:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/community/contributing/powershell-style-guide.md	✅Succeeded	View (>=powershell-5.1)

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

[github-actions]

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[learn-build-service-prod]

Learn Build status updates of commit 2a5d3dd:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/docs-conceptual/community/contributing/powershell-style-guide.md	✅Succeeded	View (>=powershell-5.1)

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