Fix missing reference TOC

[xmdanni]

PR Summary

Fix reference TOC missing when open conceptual webpages. Validated review page: https://review.learn.microsoft.com/en-us/powershell/dsc/overview?view=dsc-3.0&branch=danni-test

PR Checklist

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

[learn-build-service-prod[bot]]

Learn Build status updates of commit e8e4a9a:

:warning: Validation status: warnings

File	Status	Preview URL	Details
.openpublishing.redirection.json	:warning:Warning	View (dsc-2.0)	Details
dsc/docfx.json	:white_check_mark:Succeeded
dsc/mapping/monikerMapping.json	:white_check_mark:Succeeded

.openpublishing.redirection.json

• [Warning: redirection-removed - See documentation] Redirection rule /powershell/dsc/index defined in .openpublishing.redirection.json was deleted or changed. To avoid broken links, please don't remove the redirection rule.

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[sdwheeler]

@xmdanni Thanks!