Magma cubes still spawn in Nether fortresses, even in the wrong biome

Magma cubes can spawn in fortresses, even in the Soul Sand Valley. This seems very unfitting for the Soul Sand Valley, and removes the importance of exploring the Nether Wastes.

To reproduce, use the seed -2707554613700807049 and run the following command:

/execute in minecraft:the_nether run tp @p 94 107 411

Notice that magma cubes are spawning in the Soul Sand Valley, even though there is no nearby Nether Waste.