Figure out how to keep updated the astropy-core-maintainers list

Pey-Lian pointed out this issue in an email. The maintainers list is quite stale.

Obviously for now we should just keep this up-to-date, but moving forward we need someone who's job is to keep this in sync, or some automated way to do it. 🤖

Start by reviewing the stale astropy-core-maintainers list and the surrounding project-maintainer documentation. Determine how the list should be kept current, whether an owner or an automated process is appropriate, and consider the work done when the list is updated with a sustainable maintenance approach.

Written by the indexing model from the issue text.