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_test_memory.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
@@ -19,7 +19,7 @@
   3. This notice may not be removed or altered from any source distribution.
 */
 
-/**
+/*
  *  \file SDL_test_memory.h
  *
  *  Include file for SDL test framework.
@@ -37,14 +37,14 @@ extern "C" {
 #endif
 
 
-/**
+/*
  * \brief Start tracking SDL memory allocations
  * 
  * \note This should be called before any other SDL functions for complete tracking coverage
  */
 int SDLTest_TrackAllocations(void);
 
-/**
+/*
  * \brief Print a log of any outstanding allocations
  *
  * \note This can be called after SDL_Quit()