[php-src] Issue #21519: BackedEnum::from()/tryFrom()/cases() return values having no relation to this enum

Issue: https://github.com/php/php-src/issues/21519
Author: cracksalad

### Description

The following code:

```php
<?php
declare(strict_types=1);

namespace entity\type;

enum Priority: string {
  case LOW = 'low';
  case MEDIUM = 'medium';
  case HIGH = 'high';
}
```

```php
<?php
declare(strict_types=1);

namespace recommendation;

use entity\type\Priority;
// [...]

class Handler {
  // [...]
  protected function parsePriority(MyClass $target, array $results): void {
    if(isset($results['priority']['value'])){
      $priority = Priority::tryFrom($results['priority']['value']);

      App::getLogger()->debug('got priority value', [  // Monolog logger
        'value' => $priority,
        'original' => $results['priority']['value'],
        'cases' => OptimizedActionPriority::cases()
      ]);

      if($priority !== null){
        $target->setPriority($priority);  // line 206
      }
    }
  }
// [...]
```

```php
<?php
declare(strict_types=1);

namespace entity;

use entity\type\Priority;

class MyClass {
  // [...]
  public function setPriority(Priority $priority): void {  // line 59
    // [...]
  }
  // [...]
}
```

Resulted in roughly 80 % of cases in the expected output,  but in 20 % of cases in this output:
- Log output (note that `opis/json-schema` is a dependency of my project`):
```
got priority value {"value":{"Opis\\JsonSchema\\Parsers\\Keywords\\MinimumKeywordParser":[]},"original":"medium","cases":[{"entity\\type\\OptimizedActionPriority":"low"},{"Opis\\JsonSchema\\Parsers\\Keywords\\MinimumKeywordParser":[]},{"entity\\type\\OptimizedActionPriority":"high"}]}
```
- Output:
```
[object] (TypeError(code: 0): entity\\MyClass::setPriority(): Argument #1 ($priority) must be of type entity\\type\\Priority, Opis\\JsonSchema\\Parsers\\Keywords\\MinimumKeywordParser given, called in src/recommendation/Handler.php on line 206 at src/entity/MyClass.php:59)
  [stacktrace]
  #0 src/recommendation/Handler.php(206): entity\\OptimizedAction->setPriority()
  #1 src/recommendation/[...]: recommendation\\OptimizedActionHandler->parsePriority()
  // [...]
  #6 [internal function]: {closure:scripts/worker/gearman-worker.php:131}()
  #7 scripts/worker/gearman-worker.php(221): GearmanWorker->work()
  #8 {main}
```

But I expected this output instead:
- Log output:
```
got priority value {"value":{"entity\\type\\OptimizedActionPriority":"low"},"original":"low","cases":[{"entity\\type\\OptimizedActionPriority":"low"},{"entity\\type\\OptimizedActionPriority":"medium"},{"entity\\type\\OptimizedActionPriority":"high"}]}
```

Notes:
- Sadly, I was not (yet) able to reproduce this in a minimal example and I did not find any reference online describing a similar behavior. I am a little desperate right now
- All the PHP code runs in a CLI context rather than FastCGI and is called via a Gearman worker (although the observed behavior should not happen, regardless of the context, I guess)
- The observed `$priority` values are either correct or randomly chosen class instances, that were used by the same script during the same execution. So, it might be a memory access issue?!
- The real example above is especially weird, since the "low" value from `cases()` is actually correct, while the `tryFrom("low")` value is not. You see the randomness here?
- Same behavior is to observe replacing `tryFrom()` with `from()` (and no `ValueError` is thrown)
- I tried renaming the enum (I assumed a name collision of some sort), although I can not rename the values since they need to match the API responses

### PHP Version

```plain
Tested with

PHP 8.4.19 (cli) (built: Mar 10 2026 15:51:04) (NTS gcc x86_64)
Copyright (c) The PHP Group
Built by Remi's RPM repository <https://rpms.remirepo.net/> #StandWithUkraine
Zend Engine v4.4.19, Copyright (c) Zend Technologies
    with Zend OPcache v8.4.19, Copyright (c), by Zend Technologies

as well as

PHP 8.3.30 (cli) (built: Jan 13 2026 22:36:55) (NTS gcc x86_64)
Copyright (c) The PHP Group
Zend Engine v4.3.30, Copyright (c) Zend Technologies
    with Zend OPcache v8.3.30, Copyright (c), by Zend Technologies
```

### Operating System

AlmaLinux 9