DOC: update release process maintainer guide
A small things I noticed that could use some update or clarification while releasing 2.3.1. 

cc @mroeschke can you check that this confirms with your experience when releasing 2.3.0?
@jorisvandenbossche one thing that I used to do during pre-release is ensure that the release notes between the backport and the main branch were in sync.

Discrepancies can arise if backports are missed or merge conflicts on the backport were perhaps not resolved correctly, so this used to be a beneficial check.

IIRC we had some issues with the 2.3.0 release that would have been picked up if this was done. As well as the release process instructions, I used to use a release checklist on the release issue.

Maybe, while updating the process, you could add something to "Update and clean release notes for the version to be released, including:" section? Thanks @jorisvandenbossche 