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_config_windows.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
@@ -99,9 +99,11 @@ typedef unsigned int uintptr_t;
 #define HAVE_D3D11_H 1
 #define HAVE_ROAPI_H 1
 #endif
-#if defined(WDK_NTDDI_VERSION) && WDK_NTDDI_VERSION > 0x0A000008 /* 10.0.19041.0 */
+#if defined(__has_include)
+#if __has_include(<d3d12.h>) && __has_include(<d3d12sdklayers.h>)
 #define HAVE_D3D12_H 1
 #endif
+#endif
 #if defined(_WIN32_MAXVER) && _WIN32_MAXVER >= 0x0603  /* Windows 8.1 SDK */
 #define HAVE_SHELLSCALINGAPI_H 1
 #endif