Update dependency phpunit/phpunit to v9.6.26

Author: renovate[bot]

composer.json

@@ -20,7 +20,7 @@
     },
     "require-dev": {
         "squizlabs/php_codesniffer": "3.7.1",
-        "phpunit/phpunit": "9.5.14",
+        "phpunit/phpunit": "9.6.26",
         "clivern/phpcs": "1.0.2"
     },
     "autoload": {