Not working with central package management CPM

[pjcable]

NugetSwitcher has worked well for us for the past year but we've recently converted to using Central Package Management

https://learn.microsoft.com/en-us/nuget/consume-packages/central-package-management

When switching to projects we get the error:

`Caller: Callback. Message: Cannot modify an evaluated object originating in an imported file "c:\SourceCode\TheApp\Directory.Packages.props".`

This leaves us with duplicate imports so we get XXX is ambiguous in the namespace YYY