Kelp and seagrass can generate floating on submerged beached shipwrecks

Steps to reproduce:

1. Generate a standard world with the seed -5068785406039679215.

2. Execute

   /execute in minecraft:overworld run tp @s 6646.25 58.78 -2227.14 -300.53 31.35

3. ❌ Kelp and seagrass can be seen floating over slabs and trapdoors. There is also some kelp on fences where it cannot be placed by the player.

This was not the case in 26.2. The bug does not seem to affect normal shipwrecks, only beached ones submerged in water.