How to set Repository in custom nuspec

I'm using a custom NuSpec file with an SDK project like this, and can't get sourcelink to work correctly.

.csproj snippet:
```xml

true
Pack.nuspec
$(NuspecProperties);Repository=$(RepositoryUrl)

```

Pack.nuspec snippet:
```xml

$Repository$

```

But the `repository` isn't set in the resulting .nupkg's .nuspec file. Any tips? Is this possible?

My other projects in the same solution (which don't need a custom Nuspec) have it set just fine.