[9.x] Fix enum casts arrayable behaviour

[diegotibi]

This PR fix a wrong behavoiur when an attribute is casted to an enum implementig Arrayable in comparision to the behavoiur when the same thing is done on a collection object.

Clarifying example:

Let's take this enum:

enum Status: string implements Arrayable
{
    case pending = 'pending';
    case done = 'done';
    
    /**
     * @inheritDoc
     */
    public function toArray()
    {
        return [
            'name' => $this->name,
            'value' => $this->value,
            'description' => "description of {$this->name}",
        ];
    }
}

Behaviour in a collection object:

collect(Status::pending)->toArray();
/**
[
     "name" => "pending",
     "value" => "pending",
     "description" => "description of pending",
]
*/

Behaviour in a casted model attribute:

class MyModel extends Model
{
    protected $casts = [
        'status' => Status::class
    ];
}


MyModel::first()->toArray();
/**
[
    'id' => 1,
    'status' => 'pending'
]
*/

Expected behaviour:

MyModel::first()->toArray();
/**
[
    'id' => 1,
    'status' => [
         "name" => "pending",
         "value" => "pending",
         "description" => "description of pending",
   ]
]
*/

Related issues: #40580 and #40693

[driesvints]

I definitely wouldn't expect enums to be converted to their array version. Their value should be used. The current behavior is expected imo.

[X-Coder264]

Without this change there's no point in an enum implementing Arrayable as it does nothing for enums currently - which is inconsistent with how all other Arrayable implementations are treated by Eloquent.

On the other hand I don't see much of an use case in transforming a scalar value into an array.

I guess there's no harm in letting enums behave like all other Arrayable implementations as I don't see any other use case as to why users would implement Arrayable on their enums.

[driesvints]

@X-Coder264 hmm I guess you're right about that.

[GrahamCampbell]

If this is considered a bug fix, this should probably land on Laravel 8, not 9.

[diegotibi]

@GrahamCampbell yes, you're probably right, this PR can ported to 8.x branch with no work at all. However enums are a php 8.1 feature so it's probably more usefull on 9.x branch

[GrahamCampbell]

PHP 8.1 can also be used with Laravel 8, so that's not relevant, actually.

[diegotibi]

@taylorotwell Should I make a PR on 8.x branch too, like @GrahamCampbell suggested?