Fix "Cannot access non-public property Parser::$mStripState"

Discussed under https://www.mediawiki.org/wiki/Topic:Xc6c9apmxydt7817

Bug: T333675
Change-Id: Ifd38878edfd6481de85efd716e4f954cd1e449bb
(cherry picked from commit 4212d24b49)

src/ContributionScores.php

@@ -76,7 +76,7 @@ class ContributionScores extends IncludableSpecialPage {
 		} else {
 			$output = wfMessage( 'contributionscores-invalidusername' )->text();
 		}
-		return $parser->insertStripItem( $output, $parser->mStripState );
+		return $parser->insertStripItem( $output, $parser->getStripState() );
 	}
 
 	/**