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_error.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
@@ -20,9 +20,9 @@
 */
 
 /**
- *  \file SDL_error.h
+ * # CategoryError
  *
- *  Simple error message routines for SDL.
+ * Simple error message routines for SDL.
  */
 
 #ifndef SDL_error_h_
@@ -53,9 +53,9 @@ extern "C" {
  * }
  * ```
  *
- * \param fmt a printf()-style message format string
+ * \param fmt a printf()-style message format string.
  * \param ... additional parameters matching % tokens in the `fmt` string, if
- *            any
+ *            any.
  * \returns always -1.
  *
  * \since This function is available since SDL 2.0.0.
@@ -109,8 +109,8 @@ extern DECLSPEC const char *SDLCALL SDL_GetError(void);
  * otherwise operates exactly the same as SDL_GetError().
  *
  * \param errstr A buffer to fill with the last error message that was set for
- *               the current thread
- * \param maxlen The size of the buffer pointed to by the errstr parameter
+ *               the current thread.
+ * \param maxlen The size of the buffer pointed to by the errstr parameter.
  * \returns the pointer passed in as the `errstr` parameter.
  *
  * \since This function is available since SDL 2.0.14.