fix:change primary constructor back to explicit constructor to avoid failed build in dotnet 6

Author: Fei Xu

test/Autofac.Extras.DynamicProxy.Test/ServiceMiddlewareInterfaceInterceptorsFixture.cs

@@ -57,12 +57,21 @@ public void InterceptsPublicInterfacesUseNoneGenericMethod()
         mockDecorator.Verify(e => e.Decorate(), Times.Never);
     }
 
-    public class Decorator(IPublicInterface decoratedService, IDecoratorInterface decoratorInterface) : IPublicInterface
+    public class Decorator : IPublicInterface
     {
+        private readonly IPublicInterface _decoratedService;
+        private readonly IDecoratorInterface _decoratorInterface;
+
+        public Decorator(IPublicInterface decoratedService, IDecoratorInterface decoratorInterface)
+        {
+            _decoratedService = decoratedService;
+            _decoratorInterface = decoratorInterface;
+        }
+
         public string PublicMethod()
         {
-            decoratorInterface.Decorate();
-            return decoratedService.PublicMethod();
+            _decoratorInterface.Decorate();
+            return _decoratedService.PublicMethod();
         }
     }