Wither Skeletons can only spawn on Nether Bricks

The Bug

Wither Skeletons can only spawn on Nether Bricks in Nether Fortresses. This was not the case in 1.17.1

Reproduce

• Make the wither skeleton farm design from LogicalGeekBoy on 1.17.1
• Watch the spawns
• Upgrade your world to the latest 1.18 snapshot or above
• Watch the spawns

Observed Result

No Wither Skeletons spawned in the 1.18 snapshots but did in 1.17.1

Expected Result

The Wither Skeletons would spawn the same as they did in 1.17.1