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_loadso.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
@@ -19,23 +19,25 @@
   3. This notice may not be removed or altered from any source distribution.
 */
 
+/* WIKI CATEGORY: LoadSO */
+
 /**
- *  \file SDL_loadso.h
+ * # CategoryLoadSO
  *
- *  System dependent library loading routines
+ * System-dependent library loading routines.
  *
- *  Some things to keep in mind:
- *  \li These functions only work on C function names.  Other languages may
- *      have name mangling and intrinsic language support that varies from
- *      compiler to compiler.
- *  \li Make sure you declare your function pointers with the same calling
- *      convention as the actual library function.  Your code will crash
- *      mysteriously if you do not do this.
- *  \li Avoid namespace collisions.  If you load a symbol from the library,
- *      it is not defined whether or not it goes into the global symbol
- *      namespace for the application.  If it does and it conflicts with
- *      symbols in your code or other shared libraries, you will not get
- *      the results you expect. :)
+ * Some things to keep in mind:
+ *
+ * - These functions only work on C function names. Other languages may have
+ *   name mangling and intrinsic language support that varies from compiler to
+ *   compiler.
+ * - Make sure you declare your function pointers with the same calling
+ *   convention as the actual library function. Your code will crash
+ *   mysteriously if you do not do this.
+ * - Avoid namespace collisions. If you load a symbol from the library, it is
+ *   not defined whether or not it goes into the global symbol namespace for
+ *   the application. If it does and it conflicts with symbols in your code or
+ *   other shared libraries, you will not get the results you expect. :)
  */
 
 #ifndef SDL_loadso_h_
@@ -53,7 +55,7 @@ extern "C" {
 /**
  * Dynamically load a shared object.
  *
- * \param sofile a system-dependent name of the object file
+ * \param sofile a system-dependent name of the object file.
  * \returns an opaque pointer to the object handle or NULL if there was an
  *          error; call SDL_GetError() for more information.
  *
@@ -79,8 +81,8 @@ extern DECLSPEC void *SDLCALL SDL_LoadObject(const char *sofile);
  *
  * If the requested function doesn't exist, NULL is returned.
  *
- * \param handle a valid shared object handle returned by SDL_LoadObject()
- * \param name the name of the function to look up
+ * \param handle a valid shared object handle returned by SDL_LoadObject().
+ * \param name the name of the function to look up.
  * \returns a pointer to the function or NULL if there was an error; call
  *          SDL_GetError() for more information.
  *
@@ -95,7 +97,7 @@ extern DECLSPEC void *SDLCALL SDL_LoadFunction(void *handle,
 /**
  * Unload a shared object from memory.
  *
- * \param handle a valid shared object handle returned by SDL_LoadObject()
+ * \param handle a valid shared object handle returned by SDL_LoadObject().
  *
  * \since This function is available since SDL 2.0.0.
  *