Update to nuget 6.12.2.1

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#### AI description  (iteration 1)
#### PR Classification
Dependency update

#### PR Summary
This pull request updates the NuGet dependencies to version 6.12.2-rc.1.
- Updated NuGet dependencies in `eng/Version.Details.xml` to version 6.12.2-rc.1.
- Updated NuGet package versions in `eng/Versions.props` to version 6.12.2-rc.1.