Understandable in your situation.
I go out by myself, all night. I will sleep in during the day, and go from midnight to 7am sometimes when I'm out having fun. I make it a day, so to speak. I work nights, so being up all night is normal for me most of the time. I go off in rural areas. I'm more worried about the wildlife than I am of people. But then again, in my country, you can carry a big gun if you are worried about anything at all. I know that's different in the UK. I'm sure in France you won't be able to take your camera and a shotgun out into a field at night without one form of trouble or another, hah.
To get people interested in staying up all night with you, you have to turn it into more than just a photography shoot. I find camping does the trick. As you expect to be there late and stay the night, so while they sleep, you shoot. Go far enough out where you can have a fire. I've done shoots near a fire, and it was not a problem, didn't mess with my shots because it didn't emit enough light to reflect on anything (clouds) to ruin shots. Otherwise, find another soul who is into astrophotography. I'm sure you have camera/photography forums that cater to people in France, as a means to hook up with someone with similar interests.
I prefer to be alone mostly, due to my rigorous planning, but I'd still take company if someone asked me. There's usually precious little time to be distracted when working within a window for a specific shoot. One thing I've learned doing astro, is that you have to look in advance for what you're going to shoot, monitor the weather, and plan ahead. That means you usually know the date, and time frame, for what you plan to shoot. I do not just go out on a clear night and randomly try to see what I can capture. Do that and you end up wasting precious little time between clouds, weather, etc. And miss out on objects that you really want to see in your photos. The milky way really requires planning, I plan months in advance for it to know time frames. For bodies/galaxies/DSO's, I use software to see where they will be, when, and compare to weather, and plan a day or two ahead for them. This way when I go out, I can use every minute doing captures.
Why do I stress all the planning? If you go out for 2~3 hours, and you're not very well experienced with setup, right exposure, pointing towards the right area of the sky, things you cannot plan for (random weather spikes) or foreign light you didn't plan on (other people usually... ggrrrr), you will find that in that time frame, you get very little shots, and of those, how many are truly keepers? Composition still matters, and so you might re-do a few shots after you view them. That's a lot of standing around. Use that standing around time to plan out your next shot or keep an eye on the weather or flying object.
I can't stress how many shots I've stopped due to a stupid airplane flying right into my field of view. I hate the human impact on light sometimes. So there's a lot of time lost due to just waiting for the airplanes/jets to get out of your sky. Sometimes, the traffic is heavy and you literally cannot get a shot without them for a while! When you do 4+ minute exposures like I do, this can waste literally an hour of your time!
Anyhow, get people interested by looking for a crew who wants to go camping and backpacking, and definitely look into other photographers. Seek out other astrophotographers in your area. You'd be surprised there are likely many. You can swap techniques, share gear, and share company.
Some people love to go and are just looking for a reason--you asking could be that reason.
I know if someone actually asked to hang out with me all night, I'd take them, simply because no one ever does (Florida). Though in my area, people do "fishing" buddies all time. We meet/arrange on a forum dedicated to fishing in Florida, and meet up. The same thing exists for photography actually. Just look into it in your country. Google away!