Add a nuget.config file to try to fix CI

src/Abc.Zebus.sln

@@ -19,6 +19,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "@ Solution Items", "@ Solut
 		..\RELEASE_NOTES_DIRECTORY.md = ..\RELEASE_NOTES_DIRECTORY.md
 		..\azure-pipelines.yml = ..\azure-pipelines.yml
 		..\ReleaseSteps.md = ..\ReleaseSteps.md
+		nuget.config = nuget.config
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Abc.Zebus.Contracts", "Abc.Zebus.Contracts\Abc.Zebus.Contracts.csproj", "{507A4411-DB8A-4663-A491-CCA29854B890}"

src/nuget.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+  </packageSources>
+</configuration>