Error: your composer.lock file is not up to date.

Error: your composer.lock file is not up to date. Run "composer update" to install newer dependencies1

This is a conflict caused by MediaWiki due to how it is using "composer.json" file for its own purpose.2 It may occur when running MediaWiki's "update.php" maintenance script. Just add the --skip-external-dependencies flag to your command, e.g.:

php maintenance/update.php --skip-external-dependencies