Fix invalid feedback_system value in docfx.json

[ShreyasSar26]

Summary

Fixes the recurring OpenPublishing build warning on docs/docfx.json:

Invalid value for feedback_system: GitHub. The value must be Standard, OpenSource, or None.

GitHub is a deprecated value. This repo collects docs feedback through GitHub Issues (feedback_github_repo is set to SharePoint/sp-dev-docs), so the correct modern value is OpenSource, which preserves the existing GitHub-Issues feedback behavior while clearing the warning.

Change

• docs/docfx.json line 45: "feedback_system": "GitHub" → "feedback_system": "OpenSource"

Not included (intentionally)

The build also reports two ms.subservice warnings on general-development/** and spfx/** (sharepoint-framework not valid with ms.service: sharepoint-online). Those are unrelated to this change and may be intentional, so I've left them for the SPFx doc owners to decide.

Testing

Single global-metadata value change; no content or link changes. Feedback widget continues to route to GitHub Issues via the existing feedback_github_repo.

[learn-build-service-prod]

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[learn-build-service-prod]

Learn Build status updates of commit 2a0f46d:

⚠️ Validation status: warnings

File	Status	Preview URL	Details
docs/docfx.json	⚠️Warning		Details

docs/docfx.json

• Line 68, Column 59: [Warning: ms-service-subservice-invalid - See documentation] Invalid value for 'ms.subservice': 'sharepoint-framework' is not valid with 'ms.service' value 'sharepoint-online'.
• Line 69, Column 44: [Warning: ms-service-subservice-invalid - See documentation] Invalid value for 'ms.subservice': 'sharepoint-framework' is not valid with 'ms.service' value 'sharepoint-online'.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.

[Andrew Connell (andrewconnell)]

This is a significant change that I'd prefer Vesa Juvonen (@VesaJuvonen) make the call on.