Sandbox46: reference Test classes rather than include

tests/ImageSharp.Sandbox46/ImageSharp.Sandbox46.csproj

@@ -14,14 +14,14 @@
     <IsTestProject>false</IsTestProject>
   </PropertyGroup>
 
-  <ItemGroup>
-    <Compile Include="..\ImageSharp.Tests\**\*.cs" Link="Tests\%(RecursiveDir)%(Filename)%(Extension)" />
-  </ItemGroup>
-
   <ItemGroup>
     <PackageReference Include="Magick.NET-Q16-AnyCPU" />
     <PackageReference Include="Moq" />
     <PackageReference Include="System.Drawing.Common" />
   </ItemGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="..\ImageSharp.Tests\ImageSharp.Tests.csproj" />
+  </ItemGroup>
+
 </Project>

tests/ImageSharp.Tests/AssemblyInfo.cs

@@ -0,0 +1,3 @@
+using System.Runtime.CompilerServices;
+
+[assembly:InternalsVisibleTo("SixLabors.ImageSharp.Sandbox46")]