Add PHP 8.4 test

Author: micheh

.github/workflows/main.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-versions: ['7.4']
+        php-versions: ['7.4', '8.4']
         dependencies:
           - lowest
           - highest

composer.json

@@ -23,7 +23,7 @@
     },
     "require-dev": {
         "phpstan/phpstan": "^2.0",
-        "phpunit/phpunit": "^8.0 || ^9.0",
+        "phpunit/phpunit": "^8.5.14 || ^9.0",
         "squizlabs/php_codesniffer": "^3.3.1"
     },
     "autoload": {