Bump slevomat/coding-standard dev dependency

Author: jmikola

composer.json

@@ -17,7 +17,7 @@
         "phpunit/phpunit": "^9.5",
         "scrutinizer/ocular": "^1.8.1",
         "squizlabs/php_codesniffer": "^3.6",
-        "slevomat/coding-standard": "^7.0"
+        "slevomat/coding-standard": "^8.0"
     },
     "autoload": {
         "psr-4": {