Wardens won't pathfind through lava despite they're immune to it

Related to MC-249415
The Warden, despite being immune to lava, cannot pathfind through lava when chasing the target. This is inconsistent with other mobs that are immune to lava, which will attempt to walk through it to get to the player if there is no other option. This may lead to more cheesable situations for the Warden in the Deep Dark.