build: explicit nuget references

Author: Danielku15

test/dotnet/NuGet.config

@@ -5,6 +5,8 @@
     <add key="repositoryPath" value="../../.nuke/temp/packages" />
   </config>
   <packageSources>
+    <clear />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
     <add key="local" value="../../dist/nupkgs" />
   </packageSources>
 </configuration>