Tuff brick stairs are invisible on dynmap

[Brokkonaut]

Issue Description: tuff brick stairs (and maybe other tuff brick blocks, like walls, slabs) are invisible on the dynmap, rendered as air

• Dynmap Version: 3.7-SNAPSHOT-949

• Server Version: Paper 1.21.1 - Build 119

• [x] I have looked at all other issues and this is not a duplicate

• [x] I have been able to replicate this

[surfrock66]

Just to confirm, we're on 3.7 beta 7. I cannot see tuff brick slabs/stairs in a straight down flat map (but I can see full blocks):

However in isometric views, I can see the blocks if I view pointing SouthEast:

But they do not render in isometric facing NorthWest:

[shaijana]

I already fixed this in June with PR #4124, which is still not merged.