Add IsPublishable to all projects

src/Tribufu/Tribufu.csproj

@@ -8,7 +8,7 @@
         <AppDesignerFolder>Properties</AppDesignerFolder>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
         <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
-        <ImplicitUsings>enable</ImplicitUsings>
+        <IsPublishable>false</IsPublishable>
         <Nullable>annotations</Nullable>
         <OutputType>Library</OutputType>
         <TargetFrameworks>net6.0</TargetFrameworks>

src/Tribufu/TribufuApi.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Tribufu. All Rights Reserved.
 // SPDX-License-Identifier: MIT
 
+using System;
 using System.Net;
 using System.Runtime.InteropServices;
 using Tribufu.Generated.Api;