Fix Phan failure in backfillUnreadWikis
Fix Phan failure in backfillUnreadWikis

Phan says:
maintenance/backfillUnreadWikis.php:51 PhanTypeMismatchArgumentNullable Argument 1 ($userIdentity) is $lookup->localUserFromCentralId($row->euw_user, CentralIdLookup::AUDIENCE_RAW) of type ?\MediaWiki\DAO\WikiAwareEntity|?\MediaWiki\User\UserIdentity but \MediaWiki\User\UserFactory::newFromUserIdentity() takes \MediaWiki\User\UserIdentity defined at ../../includes/user/UserFactory.php:166 (expected type to be non-nullable)

Follow-up to 64531785a629be6df287ab954e55b1e0a736d65f.

Change-Id: I261e87d16bc23e9f1b5d3385553c5899632c9127

wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo