Bing wallpaper fix

Just a quick bugfix for BingWallpaper. Passing in the StartupUri.Scheme allows it to work better over https so you can get a secure lock.

string url = String.Format($”{Application.StartupUri.Scheme}://www.bing.com/HPImageArchive.aspx?format=js&n={Math.Max(count, 1)}&mkt=en-US”);

list.Add($”{Application.StartupUri.Scheme}://www.bing.com{img.url}”);