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_main.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
@@ -25,9 +25,9 @@
 #include "SDL_stdinc.h"
 
 /**
- *  \file SDL_main.h
+ * # CategoryMain
  *
- *  Redefine main() on some platforms so that it is called by SDL.
+ * Redefine main() on some platforms so that it is called by SDL.
  */
 
 #ifndef SDL_MAIN_HANDLED
@@ -129,14 +129,14 @@
  *
  *  The application's main() function must be called with C linkage,
  *  and should be declared like this:
- *  \code
+ *  ```c
  *  #ifdef __cplusplus
  *  extern "C"
  *  #endif
  *  int main(int argc, char *argv[])
  *  {
  *  }
- *  \endcode
+ *  ```
  */
 
 #if defined(SDL_MAIN_NEEDED) || defined(SDL_MAIN_AVAILABLE)
@@ -149,7 +149,7 @@ extern "C" {
 #endif
 
 /**
- *  The prototype for the application's main() function
+ * The prototype for the application's main() function
  */
 typedef int (*SDL_main_func)(int argc, char *argv[]);
 extern SDLMAIN_DECLSPEC int SDL_main(int argc, char *argv[]);
@@ -222,8 +222,8 @@ extern DECLSPEC void SDLCALL SDL_UnregisterApp(void);
 /**
  * Initialize and launch an SDL/WinRT application.
  *
- * \param mainFunction the SDL app's C-style main(), an SDL_main_func
- * \param reserved reserved for future use; should be NULL
+ * \param mainFunction the SDL app's C-style main(), an SDL_main_func.
+ * \param reserved reserved for future use; should be NULL.
  * \returns 0 on success or -1 on failure; call SDL_GetError() to retrieve
  *          more information on the failure.
  *
@@ -238,10 +238,10 @@ extern DECLSPEC int SDLCALL SDL_WinRTRunApp(SDL_main_func mainFunction, void * r
 /**
  * Initializes and launches an SDL application.
  *
- * \param argc The argc parameter from the application's main() function
- * \param argv The argv parameter from the application's main() function
- * \param mainFunction The SDL app's C-style main(), an SDL_main_func
- * \return the return value from mainFunction
+ * \param argc The argc parameter from the application's main() function.
+ * \param argv The argv parameter from the application's main() function.
+ * \param mainFunction The SDL app's C-style main(), an SDL_main_func.
+ * \return the return value from mainFunction.
  *
  * \since This function is available since SDL 2.0.10.
  */
@@ -254,8 +254,8 @@ extern DECLSPEC int SDLCALL SDL_UIKitRunApp(int argc, char *argv[], SDL_main_fun
 /**
  * Initialize and launch an SDL GDK application.
  *
- * \param mainFunction the SDL app's C-style main(), an SDL_main_func
- * \param reserved reserved for future use; should be NULL
+ * \param mainFunction the SDL app's C-style main(), an SDL_main_func.
+ * \param reserved reserved for future use; should be NULL.
  * \returns 0 on success or -1 on failure; call SDL_GetError() to retrieve
  *          more information on the failure.
  *