feat : fixing create invoice tests failures

tests/ZCommerce.Application.UnitTests/Invoices/Handlers/CreateInvoiceCommandHandlerTest.cs

@@ -17,13 +17,7 @@ public class CreateInvoiceCommandHandlerTest
     {
         private readonly Mock<IApplicationContext> _context = new();
         private readonly Mock<IMapper> _mapper = new();
-        private readonly IMediator _mediator;
-
-        public CreateInvoiceCommandHandlerTest(IMediator mediator)
-        {
-            _mediator = mediator;
-        }
-
+
         [Fact]
         public async Task CreateInvoice_WithValidObject_ReturnInvoiceId()
         {