[php-src] Issue #10043: WeakMap prevents garbage collection

Issue: https://github.com/php/php-src/issues/10043 Author: nicolas-grekas ### Description I have a situation where I create an object graph similar to this one: ```php class Canary extends stdClass { public function __construct(public string $name) { } function __destruct() { echo $this->name."\n"; } } $container = new Canary('container'); $canary = new Canary('canary'); $container->canary = $canary; $map = new \WeakMap(); $map[$canary] = $container; echo 1; unset($container, $canary); gc_collect_cycles(); echo 2; ``` Resulted in this output: ``` 12 container canary ``` But I expected this output instead: ``` 1container canary 2 ``` Commenting the $map[$canary] = $container; line generates the expected output. A simpler reproducer is this one: ``` $canary = new Canary('canary'); $map = new \WeakMap(); $map[$canary] = $canary; echo 1; unset($canary); gc_collect_cycles(); echo 2; ``` Which resulted in this output: ``` 12 canary ``` But I expected this output instead: ``` 1canary 2 ``` ### PHP Version PHP >= 8.0 ### Operating System _No response_