Mannequins spawn as pigs when attempting to spawn from world generation using data packs

The Bug

If a data pack to naturally spawn Mannequins upon world generation is applied, Mannequins will spawn as pigs.

The attached datapack replaces all creature spawns with mannequin spawns, by changing the spawns of the creature category to one entry consisting of a mannequin (with a spawn count of 16).

Steps to Reproduce

1. Create a Single Biome type world with the biome set to plains, using the attached datapack (mannequin-bug-datapack.zip). Ignore the experimental settings screen.

2. Observe the surface mob spawns.

Expected Result

Mannequins spawn on the world.

Actual Result

Pigs spawn (in large quantities) instead of mannequins.