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_assert.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_assert.h
  *
  *  Include file for SDL test framework.
@@ -42,17 +42,17 @@
 extern "C" {
 #endif
 
-/**
+/*
  * \brief Fails the assert.
  */
 #define ASSERT_FAIL     0
 
-/**
+/*
  * \brief Passes the assert.
  */
 #define ASSERT_PASS     1
 
-/**
+/*
  * \brief Assert that logs and break execution flow on failures.
  *
  * \param assertCondition Evaluated condition or variable to assert; fail (==0) or pass (!=0).
@@ -60,7 +60,7 @@ extern "C" {
  */
 void SDLTest_Assert(int assertCondition, SDL_PRINTF_FORMAT_STRING const char *assertDescription, ...) SDL_PRINTF_VARARG_FUNC(2);
 
-/**
+/*
  * \brief Assert for test cases that logs but does not break execution flow on failures. Updates assertion counters.
  *
  * \param assertCondition Evaluated condition or variable to assert; fail (==0) or pass (!=0).
@@ -70,25 +70,25 @@ void SDLTest_Assert(int assertCondition, SDL_PRINTF_FORMAT_STRING const char *as
  */
 int SDLTest_AssertCheck(int assertCondition, SDL_PRINTF_FORMAT_STRING const char *assertDescription, ...) SDL_PRINTF_VARARG_FUNC(2);
 
-/**
+/*
  * \brief Explicitly pass without checking an assertion condition. Updates assertion counter.
  *
  * \param assertDescription Message to log with the assert describing it.
  */
 void SDLTest_AssertPass(SDL_PRINTF_FORMAT_STRING const char *assertDescription, ...) SDL_PRINTF_VARARG_FUNC(1);
 
-/**
+/*
  * \brief Resets the assert summary counters to zero.
  */
 void SDLTest_ResetAssertSummary(void);
 
-/**
+/*
  * \brief Logs summary of all assertions (total, pass, fail) since last reset as INFO or ERROR.
  */
 void SDLTest_LogAssertSummary(void);
 
 
-/**
+/*
  * \brief Converts the current assert summary state to a test result.
  *
  * \returns TEST_RESULT_PASSED, TEST_RESULT_FAILED, or TEST_RESULT_NO_ASSERT