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_test_md5.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
@@ -19,7 +19,7 @@
   3. This notice may not be removed or altered from any source distribution.
 */
 
-/**
+/*
  *  \file SDL_test_md5.h
  *
  *  Include file for SDL test framework.
@@ -77,7 +77,7 @@ extern "C" {
 
 /* ---------- Function Prototypes ------------- */
 
-/**
+/*
  * \brief initialize the context
  *
  * \param  mdContext        pointer to context variable
@@ -89,7 +89,7 @@ extern "C" {
  void SDLTest_Md5Init(SDLTest_Md5Context * mdContext);
 
 
-/**
+/*
  * \brief update digest from variable length data
  *
  * \param  mdContext       pointer to context variable
@@ -105,7 +105,7 @@ extern "C" {
                  unsigned int inLen);
 
 
-/**
+/*
  * \brief complete digest computation
  *
  * \param mdContext     pointer to context variable