I just experienced this myself when doing a list within a table cell. Not sure why, but it’s not extremely clean html rendered when we’ve got a block element like <ul> within a line element <span> within a cell element <td>.
With that being said though, I couldn’t find any straight clues in the CSS as to why there was this extra spacing in the lists. However, themes like Github theme and Minimal is capable of removing it, so it is doable, but I just don’t know where to do it.