This PR was merged into the 6.3 branch.

Discussion
----------

Fix order array sum normalizedData and nestedData

| Q             | A
| ------------- | ---
| Branch?       | 6.3
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | #51823
| License       | MIT

### Description

With the update of Serializer to 6.3.5, some deserialization of array to objects does behave differently (changed order of priority of configuration via attribute `#[SerializedPath]` vs. property name, when there is a key on root level with the same name as the private property.

Related to #49700.

### How to reproduce

Example to explain changed behavior:

```json
{
  "data": {
    "item": {
      "id": "id-1"
    }
  },
  "id": "id-2"
}
```

```php
final class SomeEvent
{
    #[SerializedPath('[data][item][id]')]
    public string $id;
}
```

Before 6.3.5, the value of the id was `id-1`, with the change of #49700, the value of the id becomes `id-2`.

#49700 changes `array_merge` with `array + array`. It seems that the problem stated above is related to the fact that array_merge does overwrite keys differently than array + array:

```php
$a = ['key' => 'value-a'];
$b = ['key' => 'value-b'];

var_dump(array_merge($a, $b));
// Results in:
// array(1) {
//   ["key"]=>
//   string(7) "value-b"
// }

var_dump($a + $b);
// Results in:
// array(1) {
//   ["key"]=>
//   string(7) "value-a"
// }
```

### Solution

As `array_merge` does behave slightly differently that array + array, the solution could be to switch array order to:
```diff
- $normalizedData = $normalizedData + $nestedData;
+ $normalizedData = $nestedData + $normalizedData;
```

This would result in the same, while keeping the fix (#49700) for the numeric key value

Commits
-------

67f49d4 Fix order array sum normalizedData and nestedData