workload update failures in 8.0.1xx and 8.0.4xx builds

This appears to be happening for all [dotnet-sdk-unofficial-ci runs](https://dev.azure.com/dnceng/internal/_build?definitionId=1472&_a=summary) the past month for both the 8.0.1xx and 8.0.4xx PRs.

```
Exec
Assembly = Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Parameters
Environment Variables passed to tool:
DOTNET_CLI_HOME=D:\a\_work\1\s\artifacts\tmp\Release\
CommandLineArguments = D:\a\_work\1\s\artifacts\bin\redist\Release\dotnet\dotnet workload update --from-rollback-file D:\a\_work\1\s\artifacts\bin\redist\Release\dotnet\TestRollback.json
Installing workload manifest microsoft.net.workload.mono.toolchain.current version 8.0.27...
Workload installation failed. Rolling back installed packs...
Workload update failed: Failed to install manifest microsoft.net.workload.mono.toolchain.current version 8.0.27: Response status code does not indicate success: 401 (Unauthorized)..
Errors
D:\a\_work\1\s\src\Layout\redist\targets\OverlaySdkOnLKG.targets(97,5): error MSB3073: The command "D:\a\_work\1\s\artifacts\bin\redist\Release\dotnet\dotnet workload update --from-rollback-file D:\a\_work\1\s\artifacts\bin\redist\Release\dotnet\TestRollback.json" exited with code 1. [D:\a\_work\1\s\src\Layout\redist\redist.csproj]
```