Why can't I install this NuGet package

I don't unserstand why can't I install nuget package

Microsoft.CodeAnalysis.CSharp.SourceGenerators.Testing v1.1.1

Microsoft.CodeAnalysis.CSharp.SourceGenerators.Testing v1.1.1

when I got already installed in another project:

Microsoft.CodeAnalysis.CSharp.Workspaces v4.9.2

Microsoft.CodeAnalysis.CSharp.Workspaces v4.9.2

Why can't I install this NuGet package - C#