chore(deps): bump and cap to slevomat/coding-standard to v8.15 (#155)

Author: simPod

composer.json

@@ -16,7 +16,7 @@
     "require": {
         "php": "^8.3",
         "doctrine/coding-standard": "^12.0",
-        "slevomat/coding-standard": "^8.15",
+        "slevomat/coding-standard": "8.15",
         "squizlabs/php_codesniffer": "^3.11.2"
     },
     "require-dev": {