Say what version of NuGet auditSources is available in config reference

[zivkan]

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[learn-build-service-prod]

Learn Build status updates of commit 86e31cc:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/concepts/Auditing-Packages.md	✅Succeeded	View
docs/reference/errors-and-warnings/NU1901-NU1904.md	✅Succeeded	View
docs/reference/nuget-config-file.md	✅Succeeded	View
docs/release-notes/NuGet-6.12.md	✅Succeeded	View

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