dev-master hasn't been updated since 2018-04-18 02:14 UTC
Could someone with access to Packagist and GitHub add the hook as described?
Add the mediawiki repository to your composer.json by executing:
composer config repositories.mediawiki vcs https://github.com/wikimedia/mediawiki
This will clone the repo and analyze all of the branches and tags and build the metadata based on that (effectively the same thing packagist is doing).