No-one might even look.
As a hiring manager, I don't necessarily go and look in any detail at the GitHub histories of anyone applying for a job with me. If they mention it, I might if I'm curious, but I have a hiring procedure (as most companies do) that doesn't depend on someone even having a GitHub project, so I usually wouldn't look. Others may differ, of course.
If they look, they might not notice.
If I am looking at someone's GitHub, I'm going to be doing it to assess their technical abilities. It feels very unlikely that I would look too closely at something that wasn't code they'd checked in. If I did go and look at bug reports they'd raised, then I might not even realise what the thing they raised the report for is about (if it's a project called ThisSiteIsDefinitelyNotSafeForWork, then maybe. If it's just called ProjectAwesomeCodename, probably not).
If they do notice, it shouldn't matter.
It's your personal GitHub profile. You won't be using it at work so why should it matter? Perhaps if it were something illegal, but on the assumption that it's not - consenting adults can and do carry out NSFW activities when they're not at work. (The clue is in the name!) Your personal interests along those lines (if that's even what it is; for all I know, you may have been contributing on a purely technical basis without any interest in the actual content) should have no bearing on work.
Of course, I can't say it won't matter. Some people may feel entitled for whatever reason to make judgements about other people's personal lives and spare time activities. I don't know how they would justify that, and I personally would not want to work for someone like that, but I can't guarantee it won't happen.
Additionally, "NSFW" activities do exist and do happen, sometimes even in a professional capacity. I once worked with someone who spent her weekends working on a "sex chat" phoneline. It made no difference to the work she did for our company, so wasn't an issue. Also, in a former job, one of our largest customers was a company that broadcast a variety of pornographic TV channels. Well, they were a customer like any other. I suspect that most people would understand that and not hold such experience against someone who did work for them. Either of those would be much bigger things. Either way, one bug report on someone's personal GitHub account should make no difference to most - though again, no guarantees that it will never have any effect on anyone.
Do you really want to present a false front to look "professional"?
While I don't recommend talking about your spare time, potentially NSFW activities or interests at work (...obviously); actively hiding aspects of your personal life only seems likely to cause problems down the road. If somehow your contribution to the project gets discovered later, will you look like a liar? And besides, how far do you go? Do you ensure there are no photos on the internet of you with an alcoholic drink in your hand, in case a future employer frowns on drinking? Avoid wearing clothing with sports teams logos, in case a future employer supports a different team? Where does it stop?
Obligatory XKCD: https://xkcd.com/137/ (warning, NSFW language!)
In summary: in my view, there is no reason to be concerned. It'll probably never be a problem, and if it is, it's likely that the potential future employer has unreasonable views on the (lack of) separation between someone's working life and their private life.
