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_clipboard.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
@@ -20,7 +20,7 @@
 */
 
 /**
- * \file SDL_clipboard.h
+ * # CategoryClipboard
  *
  * Include file for SDL clipboard handling
  */
@@ -41,7 +41,7 @@ extern "C" {
 /**
  * Put UTF-8 text into the clipboard.
  *
- * \param text the text to store in the clipboard
+ * \param text the text to store in the clipboard.
  * \returns 0 on success or a negative error code on failure; call
  *          SDL_GetError() for more information.
  *
@@ -85,7 +85,7 @@ extern DECLSPEC SDL_bool SDLCALL SDL_HasClipboardText(void);
 /**
  * Put UTF-8 text into the primary selection.
  *
- * \param text the text to store in the primary selection
+ * \param text the text to store in the primary selection.
  * \returns 0 on success or a negative error code on failure; call
  *          SDL_GetError() for more information.
  *