The bug

When a wither shoots a wither skull, sculk sensors do not react, despite this being a projectile fired. According to the 20w49a changelog, this is a valid vibration.

How to reproduce

1. Build a bedrock box to contain the wither, in case something goes wrong:

   /fill ~ ~ ~ ~15 ~10 ~15 minecraft:bedrock hollow
   

2. Go inside of the bedrock box, and summon a wither riding a minecart:

   /summon minecraft:minecart ~ ~ ~ {Passengers:[{id:"minecraft:wither"}]}
   

3. Place a sculk sensor next to the wither
4. Use a spawn egg to summon a chicken on the opposite side of the bedrock box
5. Wait until the wither attacks the chicken by shooting wither skulls
   Notice how the sculk sensor is not activated when the wither shoots its skulls