Passengers are forced to dismount when a parrot sits on a player's shoulder

Description

Short description of the issue: When a parrot entity carrying any passengers sits on a player's shoulder, all passengers are immediately dismounted. Instead of being carried along with the parrot as part of the ShoulderEntity data, the passengers are left behind in the world at the parrot's previous location.

Steps to reproduce the issue:

1. Summon a parrot with a passenger (like a marker) to make the effect obvious:

   /summon parrot ~ ~ ~ {Passengers:[{id:"minecraft:marker",Tags:["cords"]}]}

2. Approach the parrot so it sits on your shoulder.

3. Observe the marker.

Expected result: The passenger should either be preserved within the ShoulderEntity NBT data (allowing it to appear on the shoulder with the parrot) or the game should prevent the parrot from sitting on the shoulder if it has passengers to avoid breaking the entity stack.

Actual result: The parrot successfully sits on the player's shoulder, but the passenger is instantly dismounted and remains stationary in the world, breaking the "riding" relationship.