build: Upgrade phpunit to 9.6.16

Bug: T342110
Change-Id: Iea6443c7dbb5d933f284f9ceec3d39c2910ffb16

Author: jdforrester

composer.json

@@ -26,7 +26,7 @@
 		"mediawiki/mediawiki-codesniffer": "41.0.0",
 		"mediawiki/mediawiki-phan-config": "0.12.1",
 		"php-parallel-lint/php-parallel-lint": "1.3.2",
-		"phpunit/phpunit": "9.5.28"
+		"phpunit/phpunit": "9.6.16"
 	},
 	"scripts": {
 		"test": [