Create/Update assets for version 1.21.3

data/minecraft/structure/trial_chambers/chamber/assembly/_list.json

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+{"directories":[],"files":["cover_1.nbt","cover_2.nbt","cover_3.nbt","cover_4.nbt","cover_5.nbt","cover_6.nbt","cover_7.nbt","full_column.nbt","hanging_1.nbt","hanging_2.nbt","hanging_3.nbt","hanging_4.nbt","hanging_5.nbt","left_staircase_1.nbt","left_staircase_2.nbt","left_staircase_3.nbt","platform_1.nbt","right_staircase_1.nbt","right_staircase_2.nbt","right_staircase_3.nbt","spawner_1.nbt"]}