Cobwebs in mineshafts can generate as if supported by chains

The bug

Despite not being a full block, chains support cobwebs. This can lead to a cobweb next to only chains (and no solid blocks).

How to reproduce

This seed and coordinates worked in 21w08a.

Seed: -8131653949012933360
Coordinates: /execute in minecraft:overworld run tp @s -876.69 -10.84 878.11 494.04 12.35