Upgrade to new Coding Standard

This also moves checking to PHP8 as the new default version.

Author: rdohms

.github/workflows/check-cs.yml

@@ -25,7 +25,7 @@ jobs:
     - name: Setup PHP
       uses: shivammathur/setup-php@v2
       with:
-        php-version: 7.4
+        php-version: 8.x
         coverage: none
         tools: composer, cs2pr
 

composer.json

@@ -15,7 +15,7 @@
     ],
     "require-dev": {
         "squizlabs/php_codesniffer": "^3.4",
-        "dms/coding-standard": "^8"
+        "dms/coding-standard": "^9"
     },
     "autoload": {
         "files": ["assertarraysubset-autoload.php"]