Document that SDL_SCALEMODE_PIXELART is available in 3.4.0

Fixes https://github.com/libsdl-org/sdlwiki/issues/856

include/SDL3/SDL_surface.h

@@ -86,7 +86,7 @@ typedef enum SDL_ScaleMode
     SDL_SCALEMODE_INVALID = -1,
     SDL_SCALEMODE_NEAREST,  /**< nearest pixel sampling */
     SDL_SCALEMODE_LINEAR,   /**< linear filtering */
-    SDL_SCALEMODE_PIXELART  /**< nearest pixel sampling with improved scaling for pixel art */
+    SDL_SCALEMODE_PIXELART  /**< nearest pixel sampling with improved scaling for pixel art, available since SDL 3.4.0 */
 } SDL_ScaleMode;
 
 /**