This looks like something that needs to be fixed in the script. Please file an issue on the openhabian repo. See How to file an Issue. The repo is at GitHub - openhab/openhabian: openHABian - empowering the smart home, for Raspberry Pi and Debian systems.
To do it by hand run
sudo apt-get -y --allow-downgrades -y install openhab2=2.5.0~M-1