ldc-legaulois/app/Http/Requests/UpdateSubRange.php

<?php

namespace App\Http\Requests;

class UpdateSubRange extends StoreSubRange
{
    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return \array_merge(parent::rules(), [
            'slug' => [
                'required',
                'unique:sub_ranges,slug,' . $this->subrange->id
            ]
        ]);
    }
}