Amethyst geodes can overwrite bedrock

I've been experimenting with geode configured_features and noticed that they are capable of replacing bedrock. This should not be something that happens in normal gameplay.

To reproduce

1. Install the datapack TESTING.zip
2. Run the command /locatebiome lithoscene:salt_flats
3. Teleport to y=-5
4. Observe that the bedrock is being overwritten by the geode features.

This issue also happens without using a data pack, for example at this location (from MC-214107):

Seed: -115398801428600131
Coordinates: -430 0 -2429