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_opengl.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
@@ -19,17 +19,11 @@
   3. This notice may not be removed or altered from any source distribution.
 */
 
-/**
- *  \file SDL_opengl.h
+/*
+ * This is a simple file to encapsulate the OpenGL API headers.
  *
- *  This is a simple file to encapsulate the OpenGL API headers.
- */
-
-/**
- *  \def NO_SDL_GLEXT
- *
- *  Define this if you have your own version of glext.h and want to disable the
- *  version included in SDL_opengl.h.
+ * Define NO_SDL_GLEXT if you have your own version of glext.h and want
+ * to disable the version included in SDL_opengl.h.
  */
 
 #ifndef SDL_opengl_h_