[9.x] Fixes default attribute value when using enums on model:show

[josecl]

Problem

Having an UnitEnum or BackedEnum as default attribute value in a Model, like this:

    protected $casts = [
        'status' => InvoiceStatus::class,
    ];

    protected $attributes = [
        'status' => InvoiceStatus::I_LOVE_LARAVEL,
    ];

Triggers an error on model:show command:

ERROR: Object of class App\Enums\InvoiceStatus could not be converted to string

Fix

This PR fixes it displaying the value of enums name attribute:

 status fillable ................................... integer / App\Enums\InvoiceStatus
  ⇂ default: I_LOVE_LARAVEL

[jessarcher]

Hey @josecl,

Thanks for this! I think the error will still occur with the --json flag, so it might be better to move this change to the getColumnDefault() method to fix it everywhere. I'll work up a PR now.