Run CI matrix on PHP 8.4 for PHPUnit 13 compatibility

Author: Hyunk3l

.github/workflows/php.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-version: [ '8.3', '8.4' ]
+        php-version: [ '8.4' ]
 
     steps:
     - uses: actions/checkout@v4