Prepare for PHP 8.4

Author: SakiTakamachi

CONTRIBUTING.md

@@ -350,7 +350,8 @@ Currently, we have the following branches in use:
 
 | Branch    |           |
 | --------- | --------- |
-| master    | Active development branch for PHP 8.4, which is open for backwards incompatible changes and major internal API changes. |
+| master    | Active development branch for PHP 8.5, which is open for backwards incompatible changes and major internal API changes. |
+| PHP-8.4   | Is used to release the PHP 8.4.x series. This is a current stable version and is open for bugfixes only. |
 | PHP-8.3   | Is used to release the PHP 8.3.x series. This is a current stable version and is open for bugfixes only. |
 | PHP-8.2   | Is used to release the PHP 8.2.x series. This is a current stable version and is open for bugfixes only. |
 | PHP-8.1   | Is used to release the PHP 8.1.x series. This is an old stable version and is open for security fixes only. |