Update dependency squizlabs/php_codesniffer to v4

Author: renovate[bot]

composer.json

@@ -12,7 +12,7 @@
         "mockery/mockery": "^1.5",
         "wp-phpunit/wp-phpunit": "^6.1",
         "yoast/phpunit-polyfills": "^1.0",
-        "squizlabs/php_codesniffer": "^3.7",
+        "squizlabs/php_codesniffer": "^4.0",
         "wp-coding-standards/wpcs": "^3.0"
     },
     "autoload": {