build: Upgrade ockcyp/covers-validator to 1.6.0

This is the last canary repo not specifically pinned to this version.

Change-Id: I2ca4530f9e2500072e6f4d6490c269dfd0997439

Author: jdforrester

composer.json

@@ -17,7 +17,7 @@
 	"require-dev": {
 		"mediawiki/mediawiki-codesniffer": "39.0.0",
 		"mediawiki/minus-x": "1.1.1",
-		"ockcyp/covers-validator": "1.4.0",
+		"ockcyp/covers-validator": "1.6.0",
 		"php-parallel-lint/php-console-highlighter": "1.0.0",
 		"php-parallel-lint/php-parallel-lint": "1.3.2",
 		"phpunit/phpunit": "^8.5"