Undead mobs catch fire in arid biomes from any light source, not just direct sunlight

Undead mobs (zombies, skeletons, and zombie horses) that are exposed to the sky while standing in an arid biome (e.g. desert, badlands) catch fire from nearby light sources, even though the light is not direct sunlight.

Steps to Reproduce:

1. Go to a desert or badlands biome.

2. Spawn or find a zombie, skeleton, or zombie horse that is exposed to the open sky.

3. Place a light source (e.g. a torch, lantern, or glowstone) near the mob at night, or observe during the day.

4. Observe the mob catching fire even when it should only burn from direct sunlight exposure.

Expected Result:
Undead mobs should only catch fire from direct sunlight exposure, not from nearby light sources, regardless of biome.

Actual Result:
In arid biomes, undead mobs catch fire simply from being exposed to the sky near a light source, regardless of whether it is actually daytime/sunlight causing it.