Possibly missing source packages?

Using this [Sample.csproj.txt](https://github.com/nexB/nuget-inspector/files/10841274/Sample.csproj.txt) file (renamed to /Sample.csproj) :
```

net5.0

```

I run the inspector and I get this output:

[sample.json.txt](https://github.com/nexB/nuget-inspector/files/10841290/sample.json.txt)

1. there are no "sources_packages"
2. the homepage_url listed here is often the source repo URL:
- 'pkg:nuget/Microsoft.NETCore.Platforms@3.1.0', 'https://github.com/dotnet/corefx': no source repo, but the homepage_url is a repo and this the same in all API endpoints and its nuspec for this version (this may be different for other versions) ... and even if we had a source repo, there would be an issue as to figure which part of the sources are used in https://github.com/dotnet/corefx/releases/tag/v3.1.0 (which is further more archived)
- 'pkg:nuget/System.Security.Principal.Windows@4.7.0', 'https://github.com/dotnet/corefx', same as above
- 'pkg:nuget/System.Security.AccessControl@4.7.0', 'https://github.com/dotnet/corefx', same as above
- 'pkg:nuget/Microsoft.Win32.Registry@4.7.0', 'https://github.com/dotnet/corefx', same as above
- 'pkg:nuget/System.Diagnostics.EventLog@4.7.0', 'https://github.com/dotnet/corefx', same as above
- 'pkg:nuget/Castle.Core@5.1.1', 'http://www.castleproject.org/': here none of the API endpoint seem to have anything but https://www.nuget.org/packages/Castle.Core lists a source repo as does the nuspec at https://api.nuget.org/v3-flatcontainer/castle.core/5.1.1/castle.core.nuspec but this is empty in the catalog entry https://api.nuget.org/v3/catalog0/data/2022.12.30.09.24.25/castle.core.5.1.1.json

So this is a bit messy and there is no easy way to get something clean