Very minor debug info improvements in AstropyAutosummary

This is some really minor tweaks to how AstropyAutosummary outputs debug info, inspired by changes I was making as part of #1826 .  Honestly, probably no one else cares about this, so I'll just merge it if the tests pass, but I'll mark it 0.3.1 in case we get some bug reports down the road that this will help diagnose.