Made unit tests more resiliant to config changes

UnitTests/FileServices/FileDialogTests.cs

@@ -571,6 +571,11 @@ public class FileDialogTests (ITestOutputHelper output)
 
     private FileDialog GetInitializedFileDialog ()
     {
+
+        Window.DefaultBorderStyle = LineStyle.Single;
+        Dialog.DefaultButtonAlignment = Alignment.Center;
+        Dialog.DefaultBorderStyle = LineStyle.Single;
+
         var dlg = new FileDialog ();
         Begin (dlg);
 
@@ -579,6 +584,10 @@ public class FileDialogTests (ITestOutputHelper output)
 
     private FileDialog GetLinuxDialog ()
     {
+        Window.DefaultBorderStyle = LineStyle.Single;
+        Dialog.DefaultButtonAlignment = Alignment.Center;
+        Dialog.DefaultBorderStyle = LineStyle.Single;
+
         // Arrange
         var fileSystem = new MockFileSystem (new Dictionary<string, MockFileData> (), "/");
         fileSystem.MockTime (() => new (2010, 01, 01, 11, 12, 43));