Fixed test build

Include both .NET 6 and .NET 7 versions of the tests

Tapeti.Tests/Client/RabbitMQFixture.cs

@@ -1,6 +1,4 @@
-// Do not include in the Release build for AppVeyor due to the Docker requirement
-#if DEBUG
-using System;
+using System;
 using System.Threading.Tasks;
 using Docker.DotNet;
 using Docker.DotNet.Models;
@@ -79,4 +77,3 @@ namespace Tapeti.Tests.Client
         }
     }
 }
-#endif

appveyor.yml

@@ -36,6 +36,7 @@ test:
   assemblies:
     only:
       - Tapeti.Tests\bin\Release\net6.0\Tapeti.Tests.dll
+      - Tapeti.Tests\bin\Release\net7.0\Tapeti.Tests.dll
   categories:
     except:
       - Requires Docker