Update dependency phpunit/phpunit to v9.6.7

Author: renovate[bot]

composer.json

@@ -30,7 +30,7 @@
     "sj-i/phpdoc-type-reader": "0.1.1"
   },
   "require-dev": {
-    "phpunit/phpunit": "9.5.10",
+    "phpunit/phpunit": "9.6.7",
     "squizlabs/php_codesniffer": "3.6.1",
     "php-coveralls/php-coveralls": "2.4.3",
     "vimeo/psalm": "4.10.0",