It is so very extremely rare that there is so little you can change that you can only make a less than 6 character edit. For example, in your question itself here you are using
inline code when you aren't using code so would have been better to just put it in "quotation marks".
It's worth noting that the limit is there for a reason; it is to make <2k "new" editors pay extra careful attention when editing to make sure they fix everything possible. Only noticed one typo? Why not go back and read the post again to be sure there isn't something else that could be improved?
Now in the extremely rare occurrence that there isn't anything else you can do, I would strongly advise against making invisible formatting changes as advised by Valorum. It isn't an improvement and could lead to your edit being rejected for no improvement whatsoever because the bulk of your edit is the newline style change not the small typo.
Instead I suggest you don't edit it yourself. If the OP seems active, leave a comment asking them to update it. You'll be surprised how often even "inactive" OPs respond to a ping to update a typo.
You could always ping a >2k user or ask in chat as a whole; there is usually always someone lurking around in The Restaurant at the End of the Universe even if it doesn't look like anyone is actively talking.