Mushroom Blocks can't replace Leaf Litter

The Bug

Mushroom Blocks can't replace Leaf Litter blocks on generation

Reproduce

• Go to a Dark Oak Forest
• Find a Mushroom close to the ground

Observed Result

Parts of the mushroom were missing

Expected Result

Parts of the mushroom wouldn't be missing

Potential Fix

Adding Leaf Litter to the #replaceable_by_mushroom tag would fix this issue