Update mediawiki-codesniffer to 34.0.0

Version 33 is (indirectly) incompatible with PHP 8.

Author: lucaswerkmeister

composer.json

@@ -35,7 +35,7 @@
 		"ockcyp/covers-validator": "~1.1",
 		"phpmd/phpmd": "~2.6",
 		"phpunit/phpunit": "~8.0",
-		"mediawiki/mediawiki-codesniffer": "33.0.0"
+		"mediawiki/mediawiki-codesniffer": "34.0.0"
 	},
 	"autoload": {
 		"psr-4": {