Nether portals do not spawn Zombified Piglins when below Y=0

Summary:

Nether portals do not spawn Zombified Piglins when below Y=0.

Repro Steps:

Load the attached world. Set the random tick speed to 3000.

Observed results:

The portal above Y=0 spawns Zombified Piglins. The portal below Y=0 does not.

Expected result:

Both portals spawn Zombified Piglins.