I mean if you want to leave it there, you can, but there's a more polished way to do this. You could give the player the exact same skull item, but with a special tag like "{luckyBlock:1}" and then only detects items that do NOT have that tag. That will fix the spawner bug but more importantly, give the player the actual skull, and it looks nicer than a zombie egg and gives the player a hint of what the lucky block looks like.
