Couldn't get photos of the night sky since it got cloudy tonight, but the modded 7.0 apk didn't necessary have astrophotography mode (infinity focus setting is MIA on this build), but it does have a long exposure mode via Night Sight. You can take a regular NS shot (which is faster in 7.0), but if you have your phone steady (via tripod for example), there's a long exposure setting that automatically turns on.
Took three shots of my garage inside my car on my Pixel 2. Regular shot was pitch black (not pictured), regular NS shot, and a long exposure shot via NS. Long exposure took about 45 secs-1 min to capture.
Regular Night Sight.
Night Sight, long exposure mode.
tl;dr: Google Camera 7.0 (full version once Pixel 4 is released) has long exposure mode via Night Sight.