Unbreakable flint and steels are completely consumed when igniting a creeper

The fix for MC-257875 which was to add a check to see if the itemstack had a damageable item failed to take into account the "Unbreakable" nbt tag. Currently, if you give yourself an unbreakable flint and steel via

/give @s flint_and_steel[unbreakable={}]

and ignite a creeper with it in survival mode, the itemstack is completely removed due to the stack size being shrunk by one in Creeper#mobInteract.

The proper fix I believe is shown here in the Paper repository.