PackageReleasePackages target cannot handle multiple versions in artifacts

- [ ] This issue is blocking
- [x] This issue is causing unreasonable pain

The `PackageReleasePackages` target fails with

D:\.tools\.nuget\packages\microsoft.dotnet.arcade.sdk\11.0.0-beta.25509.1\tools\BuildReleasePackages.targets(21,5): Multiple packages of name 'Microsoft.CodeAnalysis' specified [D:\.tools\.nuget\packages\microsoft.dotnet.arcade.sdk\11.0.0-beta.25509.1\tools\AfterSolutionBuild.proj]

often when packing Roslyn locally. I have investigated and the problem is that I have accumulated several versions of packages and the target can't handle that:

That seems like a bug to me - or do I really need to remove all artifacts before running `build.cmd -pack` locally?

Start with tools/BuildReleasePackages.targets at line 21 and the referenced AfterSolutionBuild.proj, then reproduce the failure with accumulated package versions using build.cmd -pack. Confirm that PackageReleasePackages fails on multiple versions of the same package and define completion as handling those artifacts without the reported duplicate-package error.

Written by the indexing model from the issue text.