Bug#1026024: specutils: FTBFS, ModuleNotFoundError: No module named 'asdf_astropy.io'

[Ole Streicher]

Control: reassign -1 src:asdf-astropy 0.3.0-1
Control: affects -1 src:specutils
This is a bug in the current python3-asdf-astropy package that is 
incomplete. However, according to #1025434 the cause for the issue is 
probably in python3-installer.