Note that 1.40 is not yet close to ready - https://phabricator.wikimedia.org/T340939 - but the 1.39.4 security release is being prepared: https://phabricator.wikimedia.org/T332786
Unfortunately the above process is currently manual, but it looks like the goal is to automate it per https://phabricator.wikimedia.org/T345564, bringing more timely updates in the future.
Yours distracted-by-a-fox, -- Laurence 'GreenReaper' Parry - WBUG https://GreenReaper.co.uk