Describe your suggestion

Well, because it is just like stone.

Final checklist

• I know how to properly use check boxes
• I have not used any OwO's or UwU's in this issue.

#4260 closes this (I was looking into doing it but saw this PR)

Would I be able to work on this?

sure if you want to.
just add the line Blocks.COBBLED_DEEPSLATE.asItem(), here

Deepslate should probably be added as well (because stone is already there).