testingatswt has created Issue #2783: MorphTo relation won't work when eager load if target model has different primary key in laravel-mongodb. This Jira ticket was filed by GromNaN

Issue Text:

• Laravel Version: `10.44.0`
• Laravel-mongodb Version: `4.1`
• PHP Version: `8.2.10`
• Database Driver & Version: `7.0.5`

Description:

Follow #2669

If `morphTo()` is defined on model with `$primaryKey='_id'` and target model has `$primaryKey='id'` it will return `null` when eager load

Steps to reproduce

1. I have model with morphTo relationship, here is `Entities` model, having primaryKey=_id (Unmodified)
```
class Entities extends Model
{
use HasFactory;

public function source(): MorphTo

{ return $this->morphTo(__FUNCTION__, 'source_model', 'source_id'); }

}
```
and the target model if auto increamented ID, here is what is looks like
```
class Client extends Model

{ use HasFactory, AutoIncreamentTrait; protected $primaryKey = 'id'; }

```

2. When calling the relation via eager load, it returns null,

```
Entities::with('source')->find('65f435eecd749d48b70b5c6b');
```

Expected behaviour

It should return the source as relation
```
{
"_id": "65f435eecd749d48b70b5c6b",
"source_id": 1,
"source_model": "App\\Models
Client",
"assign_date": "2024-02-25T00:00:00.000000Z",
"unassign_date": null,
"notes": null,
"updated_at": "2024-03-15T11:50:06.217000Z",
"created_at": "2024-03-15T11:50:06.217000Z",
"status": "active",
"source":

{ "_id": "65f2ec6d28c0daeb6e010c60", "id": 1, "name": "Anthony Rowe", "email": "wuqykyfuk@mailinator.com", "updated_at": "2024-03-15T11:50:06.217000Z", "created_at": "2024-03-15T11:50:06.217000Z", }

}
```

Actual behaviour

Instead, it returns null
```

{ "_id": "65f435eecd749d48b70b5c6b", "source_id": 1, "source_model": "App\\Models\\Client", "assign_date": "2024-02-25T00:00:00.000000Z", "unassign_date": null, "notes": null, "updated_at": "2024-03-15T11:50:06.217000Z", "created_at": "2024-03-15T11:50:06.217000Z", "status": "active", "source": null }

```

Proposed Solution

Below is what seems to be problem
as per this commit: https://github.com/mongodb/laravel-mongodb/pull/2669/commits/4c03ea820280c8d412d7a31e6d12a794cc928408


`$this` points to current model which is in this case `Entities::class` which is wrong since it should get the ownerKey of target model, in this case `Client`. So solution would be just pass the `null` as `$ownerKey`, laravel will pick the ownerKey by it self. I already tested it