element-uap-visualelements: fix BackgroundColor missing column

[dlech]

The "Yes" was in the wrong column. Add the extra empty column to get the right number of columns.

[prmerger-automator[bot]]

@dlech : Thanks for your contribution! The author(s) have been notified to review your proposed change.

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

Learn Build status updates of commit a38a564:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
winrt-related-src/schemas/appxpackage/uapmanifestschema/element-uap-visualelements.md	:white_check_mark:Succeeded

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[drewbatgit]

Thanks for catching this!