Non-suspended generators in suspended Fiber do not participate in GC

Description

Found this while checking if https://github.com/php/php-src/issues/9916 also happened during GC.

The following code:

<?php

class Canary {
    public function __construct(
        public readonly string $x,
    ) {
    }

    public function __destruct() {
        var_dump($this->x);
    }
}

$gen = (function() {
    $canary = new Canary('Generator dtor');
    $fiber = yield;
    Fiber::suspend();
})();

$fiber = new Fiber(function() use ($gen, &$fiber) {
    $canary = new Canary('Fiber dtor');
    $gen->send($fiber);
});
$fiber->start();

$gen = null;
$fiber = null;
gc_collect_cycles();

var_dump('Shutdown');

Resulted in this output:

string(8) "Shutdown"
string(14) "Generator dtor"
string(10) "Fiber dtor"

But I expected this output instead:

string(14) "Generator dtor"
string(10) "Fiber dtor"
string(8) "Shutdown"

PHP Version

PHP 8.1

Operating System

No response

首先运行提供的 PHP 8.1 复现程序，并跟踪 gc_collect_cycles() 期间 Fiber 和 Generator 的生命周期。调查由已暂停的 Fiber 持有的未暂停 Generator 如何参与垃圾回收；完成标准是两个析构函数都在 "Shutdown" 输出之前运行。