Players with a Step Height attribute of 0 are no longer able to move on non-full blocks while sneaking

The bug

From 1.20.5 to 1.21.4, players can sneak-move as expected. Since 1.21.5, when they sneak on non-full blocks (e.g. slabs), they cannot move if their Step Height attribute is 0.

Relates to MC-270712.

Steps to reproduce

1. Set your step_height attribute to 0:

   /attribute @s minecraft:step_height base set 0

2. Place some non-full blocks like slabs, trapdoors, etc.

3. Stand on them and try to move while sneaking.

Observed results

You cannot move at all.

Expected results

You can move normally while sneaking.