Tests: Initialize App.Client

Elwig/App.xaml.cs

@@ -53,7 +53,7 @@ namespace Elwig {
         public static string? BranchFaxNr { get; private set; }
         public static string? BranchMobileNr { get; private set; }
         public static IList<IScale> Scales { get; private set; }
-        public static ClientParameters Client { get; private set; }
+        public static ClientParameters Client { get; set; }
 
         public static bool IsPrintingReady => Html.IsReady && Pdf.IsReady;
         public static Dispatcher MainDispatcher { get; private set; }