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.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
@@ -25,7 +25,6 @@
  *  Main include header for the SDL library
  */
 
-
 #ifndef SDL_h_
 #define SDL_h_
 
@@ -70,6 +69,8 @@
 extern "C" {
 #endif
 
+/* WIKI CATEGORY: Init */
+
 /* As of version 0.5, SDL is loaded dynamically into the application */
 
 /**
@@ -130,7 +131,7 @@ extern "C" {
  * call SDL_Quit() to force shutdown). If a subsystem is already loaded then
  * this call will increase the ref-count and return.
  *
- * \param flags subsystem initialization flags
+ * \param flags subsystem initialization flags.
  * \returns 0 on success or a negative error code on failure; call
  *          SDL_GetError() for more information.
  *