* Build with .NET 5.0.408

Updating the global.json to use .NET 5.0.408 fixes the restore error:

microsoft.dotnet.arcade.sdk/5.0.0-beta.21226.1/tools/Tools.proj : error NU3028: Package 'Microsoft.DotNet.Build.Tasks.VisualStudio 5.0.0-beta.21226.1' from source 'https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json': The author primary signature's timestamp found a chain building issue: ExplicitDistrust: The trust setting for this policy was set to Deny.`

Updating the dotnet cli version in eng/Versions.props fixes
the error:

.dotnet/sdk/5.0.408/Microsoft.Common.CurrentVersion.targets(4968,5): error MSB3030: Could not copy the file ".dotnet/sdk/3.1.100/Microsoft.NETCoreSdk.BundledVersions.props" because it was not found. [src/MSBuild.Bootstrap/MSBuild.Bootstrap.csproj]

* Update to NuGet 5.11.3-rc.2

Co-authored-by: Alexander Köplinger <alex.koeplinger@outlook.com>