docs: Documentation for SDL_Swap64 was reporting the wrong return type.

Fixes #13309.

(cherry picked from commit 530639aa4a72f6480b2c8caac7ca75cd005fe8bc)

include/SDL3/SDL_endian.h

@@ -486,7 +486,7 @@ SDL_FORCE_INLINE Uint32 SDL_Swap32(Uint32 x) { return x_but_byteswapped; }
  *
  * \since This function is available since SDL 3.2.0.
  */
-SDL_FORCE_INLINE Uint32 SDL_Swap64(Uint64 x) { return x_but_byteswapped; }
+SDL_FORCE_INLINE Uint64 SDL_Swap64(Uint64 x) { return x_but_byteswapped; }
 
 /**
  * Swap a 16-bit value from littleendian to native byte order.