fix CF_DIB value (https://learn.microsoft.com/en-us/windows/win32/dataxchg/standard-clipboard-formats says that CF_DIB is equal to 8)

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -2137,7 +2137,7 @@ namespace Avalonia.Win32.Interop
             /// <summary>
             /// A memory object containing a BITMAPINFO structure followed by the bitmap bits.
             /// </summary>
-            CF_DIB = 3,
+            CF_DIB = 8,
             /// <summary>
             /// Unicode text format. Each line ends with a carriage return/linefeed (CR-LF) combination. A null character signals the end of the data.
             /// </summary>