Snow golems cannot spawn naturally using customized worldgen, and are replaced with pigs

If you create a custom biome or structure and make snow golems spawn in it using the spawners or spawn_overrides JSON objects, you will instead see pigs spawn. This has been in the game in previous updates too.

See the attached datapack, which modifies the snowy_taiga biome to only spawn snow golems as creatures.

Steps to reproduce:

1. Create a world with the following:
   → Single biome, snowy taiga
   → Use 'datapack.zip'
2. Run the following command when world loads:

   /effect give @e[type=minecraft:snow_golem] minecraft:glowing