Update SDL2 to newest version to fix 7.1 playback

This fixes 7.1 playback. Before this commit, SDL used 7.1 front audio configuration with Center Left and Center Right speakers, but without Rear speakers.

See https://github.com/libsdl-org/SDL/issues/11709 for more details.

libs/SDL2/include/SDL_scancode.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the authors be held liable for any damages
@@ -20,9 +20,9 @@
 */
 
 /**
- *  \file SDL_scancode.h
+ * # CategoryScancode
  *
- *  Defines keyboard scancodes.
+ * Defines keyboard scancodes.
  */
 
 #ifndef SDL_scancode_h_
@@ -31,16 +31,16 @@
 #include "SDL_stdinc.h"
 
 /**
- *  \brief The SDL keyboard scancode representation.
+ * The SDL keyboard scancode representation.
  *
- *  Values of this type are used to represent keyboard keys, among other places
- *  in the \link SDL_Keysym::scancode key.keysym.scancode \endlink field of the
- *  SDL_Event structure.
+ * Values of this type are used to represent keyboard keys, among other places
+ * in the SDL_Keysym::scancode key.keysym.scancode field of the SDL_Event
+ * structure.
  *
- *  The values in this enumeration are based on the USB usage page standard:
- *  https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf
+ * The values in this enumeration are based on the USB usage page standard:
+ * https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf
  */
-typedef enum
+typedef enum SDL_Scancode
 {
     SDL_SCANCODE_UNKNOWN = 0,