Wardens ignore PersistenceRequired and dig away

The bug

Wardens were fixed to be unable to despawn when named, however, the tag given to named mobs is PersistenceRequired, and wardens do not operate under this tag and instead use CustomName to check if it can dig away or not. It should instead check PersistenceRequired.

Steps to Reproduce

• Spawn a Warden in an area where it cannot be distracted.
• Modify its data to include PersistenceRequired:1b.
• Wait until it digs into the ground, ignoring the tag.

Code analysis

Warden#tick() resets the dig_cooldown if the warden has a custom name, rather than checking PersistenceRequired.