`invulnerable_time` is not retained when a mob converts to another mob, even though `Invulnerable` is

The new invulnerable_time tag is not retained upon mob conversion, even though Invulnerable is.

To reproduce

1. /summon minecraft:villager ~ ~ ~ {NoAI:1b,Invulnerable:1b,invulnerable_time:9999}

2. /summon minecraft:lightning_bolt

3. /data get entity @n[type=witch] NoAI
   ✅ The tag was retained

4. /data get entity @n[type=witch] Invulnerable
   ✅ The tag was retained

5. /data get entity @n[type=witch] invulnerable_time
   ❌ The tag was not retained