[php-src] Issue #9941: Enum syntax error when using `$this` inside a method

Issue: https://github.com/php/php-src/issues/9941 Author: foremtehan ### Description The following code: ```php <?php enum Language: int { case English = 1; public function isEnglish(): bool { return $this instanceof self::English; } } echo Language::English->value; ``` Resulted in this output: ``` Parse error: syntax error, unexpected identifier "English", expecting variable or "$" in php shell code on line 1 ``` But I expected this output instead: ``` 1 ``` Using $this is not allowed inside a enum? ### PHP Version PHP 8.1.12 ### Operating System ubuntu:latest