Players can no longer respawn on scaffolding

It's no longer possible to spawn on scaffolding after respawning was changed in 20w30a.

How to reproduce:

1. Place a bed

2. Place scaffolding in 10 surrounding floor blocks around the bed

3. Block the space above the bed

4. Use the bed to set respawn point

5. Die (/kill) and respawn

Observed Results:

Player respawns at the default world spawning location, with the following message:

"You have no home bed or respawn anchor, or it was obstructed" 

Expected Results:

Player respawns on top of scaffolding blocks. 

Screenshots/Videos:

20w29a - Can spawn on scaffolding: https://youtu.be/Hs-VzACdcv0

21w41a - Can't spawn on scaffolding: https://youtu.be/Mhu_DVlLEOM

Code Analysis:
Code analysis by @unknown can be found in this comment.