Wither cannot be teleported through the Nether / End Portal

Can confirm in 1.19.3 and 23w05a

Seems absolutely intended.

Code analysis (Mojang mappings, 23w05a): when an entity is inside an end portal or nether portal block, it checks if the entity can change dimensions. WitherBoss#canChangeDimensions() returns false, so the wither can't change dimensions.

This issue does not exist on Bedrock Edition, thus, making this a parity issue.