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_gesture.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_gesture.h
+ * # CategoryGesture
  *
- *  Include file for SDL gesture event handling.
+ * Include file for SDL gesture event handling.
  */
 
 #ifndef SDL_gesture_h_
@@ -51,7 +51,7 @@ typedef Sint64 SDL_GestureID;
  * If the parameter `touchId` is -1 (i.e., all devices), this function will
  * always return 1, regardless of whether there actually are any devices.
  *
- * \param touchId the touch device id, or -1 for all touch devices
+ * \param touchId the touch device id, or -1 for all touch devices.
  * \returns 1 on success or 0 if the specified device could not be found.
  *
  * \since This function is available since SDL 2.0.0.
@@ -64,7 +64,7 @@ extern DECLSPEC int SDLCALL SDL_RecordGesture(SDL_TouchID touchId);
 /**
  * Save all currently loaded Dollar Gesture templates.
  *
- * \param dst a SDL_RWops to save to
+ * \param dst a SDL_RWops to save to.
  * \returns the number of saved templates on success or 0 on failure; call
  *          SDL_GetError() for more information.
  *
@@ -78,8 +78,8 @@ extern DECLSPEC int SDLCALL SDL_SaveAllDollarTemplates(SDL_RWops *dst);
 /**
  * Save a currently loaded Dollar Gesture template.
  *
- * \param gestureId a gesture id
- * \param dst a SDL_RWops to save to
+ * \param gestureId a gesture id.
+ * \param dst a SDL_RWops to save to.
  * \returns 1 on success or 0 on failure; call SDL_GetError() for more
  *          information.
  *
@@ -94,8 +94,8 @@ extern DECLSPEC int SDLCALL SDL_SaveDollarTemplate(SDL_GestureID gestureId,SDL_R
 /**
  * Load Dollar Gesture templates from a file.
  *
- * \param touchId a touch id
- * \param src a SDL_RWops to load from
+ * \param touchId a touch id.
+ * \param src a SDL_RWops to load from.
  * \returns the number of loaded templates on success or a negative error code
  *          (or 0) on failure; call SDL_GetError() for more information.
  *