The ender dragon's velocity can be affected by attacks while perched

While the ender dragon is perched, its Motion tag can be affected by players' attacks, especially from weapons enchanted with Knockback, which allows a player with a spear to instantly kill it if they first cause a lot of knockback to it from the opposite side (fixed after 25w42a?).

How to reproduce:

This issue is not exclusive to the snapshot series for Mounts of Mayhem, and can be reproduced simply by checking the dragon’s Motion tag, but it’s a lot more important to fix now with spears in the game.

1. Give yourself a wooden sword enchanted with Knockback II.

2. Go to the End.

3. Execute the following command:

   /kill @e[type=minecraft:end_crystal]

4. Wait for the dragon to perch.

5. Execute the following command:

   /data get entity @n[type=minecraft:ender_dragon] Motion

6. Attack the dragon a few times with the sword.

7. Execute the command from step 4 again.
   -> ❌ The value of the Motion tag has increased towards the direction you attacked the dragon.

Expected result:

The ender dragon would not be affected by knockback-inducing attacks while perched.

Observed result:

The ender dragon accumulates all knockback it takes while perched and stores it in its Motion tag.