Create/Update assets for version 1.21.3

assets/minecraft/textures/entity/shulker/_list.json

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+{"directories":[],"files":["shulker.png","shulker_black.png","shulker_blue.png","shulker_brown.png","shulker_cyan.png","shulker_gray.png","shulker_green.png","shulker_light_blue.png","shulker_light_gray.png","shulker_lime.png","shulker_magenta.png","shulker_orange.png","shulker_pink.png","shulker_purple.png","shulker_red.png","shulker_white.png","shulker_yellow.png","spark.png"]}