For more details, see T282750#7083881.
Long story short, when the engineers need to add a config, it might be necessary to add it to wiki config as well. There should be a script to do that work.
Change 690051 had a related patch set uploaded (by Urbanecm; author: Urbanecm):
[mediawiki/extensions/GrowthExperiments@master] Add changeWikiConfig.php as a maintenance script
Change 690051 merged by jenkins-bot: