app/database/seeders/GrupoSeeder.php

<?php

namespace Database\Seeders;
use App\Models\Grupo;
use Illuminate\Database\Console\Seeds\WithoutModelEvents;
use Illuminate\Database\Seeder;

class GrupoSeeder extends Seeder
{
    /**
     * Run the database seeds.
     */
    public function run(): void
    {
        Grupo::factory()->count(8)->sequence(['grupo' => 'C','grado' => '2'],
                                                ['grupo' => 'D','grado' => '2'],
                                                ['grupo' => 'E','grado' => '2'],
                                                ['grupo' => 'A','grado' => '3'],
                                                ['grupo' => 'B','grado' => '3'],
                                                ['grupo' => 'C','grado' => '3'],
                                                ['grupo' => 'D','grado' => '3'],
                                                ['grupo' => 'E','grado' => '3'],)->create();
    }
}