[TEST] Add PHPStan deprecation rules

Author: oliverklee

composer.json

@@ -42,6 +42,7 @@
 		"php-coveralls/php-coveralls": "^2.7.0",
 		"phpstan/extension-installer": "^1.3.1",
 		"phpstan/phpstan": "^1.10.50",
+		"phpstan/phpstan-deprecation-rules": "^1.1.4",
 		"phpstan/phpstan-phpunit": "^1.3.15",
 		"phpstan/phpstan-strict-rules": "^1.5.2",
 		"phpunit/phpunit": "^8.5.36",