There is no guarantee the MediaWikiServices instance is still valid.
Other tests can reset it.
Bug: T368390
Change-Id: I92de60b2ba5fb66af957a800ce85773db58303cc
Use
$this->getServiceContainer()
instead of
MediaWikiServices::getInstance()
in maintenance and tests.
Change-Id: I845e8f083b19da093166d6551683f2013eec7bb1