Updated mediawiki/extensions
Project: mediawiki/extensions/UserMerge  5b23bb885eed0506aa84ceb59b15641a40a4b970

adds an error message if old and new user names are the same

excerpt from https://gerrit.wikimedia.org/r/#/c/77814/

Change-Id: Ieab8f5f5c908105f8abc3bd3dcfb371516628ca4