Merge of nested relationships & includes on JsonApiCollection

[d8vjork]

Replication example

Loading something twice as on a polymorphic relationship and somewhere else (included as of a nested relationship), imagine something like:

// PostController.php

public function index(JsonApiResponse $response)
{
    return $response->using(Post::with([
        'parent' => fn (MorphTo $morphTo) => $morphTo->morphWith([
            Group::class => [
                'createdBy', // this being user ID = 2
            ],
        ]),
        'author', // this being user ID = 2
        'author.avatars', // load avatars from post.author relationship thought groups will not have access to this!
    ]));
}

This will get into a race condition where author relationship (in this case could be of type user) will be different sometimes at the included data array because the user is actually the same in both relationships...

[d8vjork]

Similar issue happening but with a race-condition on the merge:

public function index(JsonApiResponse $response)
{
    return $response->using(Post::with([
        'updatedBy', // this being user ID = 2
        'author', // this being user ID = 2
        'author.avatars', // load avatars from post.author relationship thought race-condition will exclude this in favor of the first found in the array
    ]));
}

Reported by @danielperez9430