Custom dimension definitions no longer allow a specified seed

{
  "type": "minecraft:overworld",
  "generator": {
    "type": "minecraft:noise",
    "seed": 3720723036382728818,
    "settings": "minecraft:overworld",
    "biome_source": {
      "type": "minecraft:multi_noise",
      "preset": "minecraft:overworld"
    }
  }
}