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_harness.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_harness.h
  *
  *  Include file for SDL test framework.
@@ -69,7 +69,7 @@ typedef int (*SDLTest_TestCaseFp)(void *arg);
 /* !< Function pointer to a test case teardown function (run after every test) */
 typedef void  (*SDLTest_TestCaseTearDownFp)(void *arg);
 
-/**
+/*
  * Holds information about a single test case.
  */
 typedef struct SDLTest_TestCaseReference {
@@ -83,7 +83,7 @@ typedef struct SDLTest_TestCaseReference {
     int enabled;
 } SDLTest_TestCaseReference;
 
-/**
+/*
  * Holds information about a test suite (multiple test cases).
  */
 typedef struct SDLTest_TestSuiteReference {
@@ -98,7 +98,7 @@ typedef struct SDLTest_TestSuiteReference {
 } SDLTest_TestSuiteReference;
 
 
-/**
+/*
  * \brief Generates a random run seed string for the harness. The generated seed will contain alphanumeric characters (0-9A-Z).
  *
  * Note: The returned string needs to be deallocated by the caller.
@@ -109,7 +109,7 @@ typedef struct SDLTest_TestSuiteReference {
  */
 char *SDLTest_GenerateRunSeed(const int length);
 
-/**
+/*
  * \brief Execute a test suite using the given run seed and execution key.
  *
  * \param testSuites Suites containing the test case.