Image-reviewer is a user group used in Wikimedia Commons and fawiki. User groups are all defined in lowercase in code. We should
- rename the group where it is used in InitialiseSettings.php and elsewhere in wmf-config.
- rename the keys to use lowercases in WikimediaMessages / cherry-pick and merge to the current wmf branch(es).
- migrate existing members using the migrateUserGroups.php maintenance script
This needs to be done all in the same SWAT window to avoid issues so I'll need some time to find the appropriate time to do it right.