Declare PHP 8.4 as the newest supported version

As the comment indicates, this includes partially supported
versions. PHP-Parser includes support for all parts of PHP 8.4
that have landed in php-src.

lib/PhpParser/PhpVersion.php

@@ -43,7 +43,7 @@ public static function fromComponents(int $major, int $minor): self {
      * if it is still under development.
      */
     public static function getNewestSupported(): self {
-        return self::fromComponents(8, 3);
+        return self::fromComponents(8, 4);
     }
 
     /**