Update to phpunit ^9.6

Author: sirreal

composer.json

@@ -42,7 +42,7 @@
 		"psr/log"                  : "~1.0"
 	},
 	"require-dev" : {
-		"phpunit/phpunit": "~8",
+		"phpunit/phpunit": "^9.6",
 		"spatie/phpunit-watcher": "^1.23",
 		"yoast/phpunit-polyfills": "^1.0"
 	},