[HttpKernel] fixes RequestDataCollector bug, visible on Drupal8

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | 

In Drupal8 ```$request->attributes->all()``` returns an array with a 0 key whose value is the ```Drupal\user\Entity\User```

```php
array(
 0 => Drupal\user\Entity\User,
 ...
)
```

```('_route' == $key && is_object($value))``` is therefore true which provokes an exception:

```php
FatalErrorException: Error: Call to undefined method Drupal\user\Entity\User::getPath() in [...]/RequestDataCollector.php line 54
```

This patch corrects this with a simple replacement of == by ===