[8.x] Fix retry command for encrypted jobs

[willbrowningme]

When using the new Illuminate\Contracts\Queue\ShouldBeEncrypted interface on a job if you run the php aritsan queue:retry command you get the following error:

unserialize(): Error at offset 0 of x bytes

This is because the job's command is not decrypted before being unserialized.

Steps to reproduce:

1. Create any queable job that implements the ShouldBeEncrypted interface
2. Call $this->fail() inside the job
3. Run php artisan queue:retry <job-id>

This pull request fixes the issue by checking if the payload's command is encrypted before trying to unserialize it.

The code is taken from the getCommand(array $data) method in Illuminate\Queue\CallQueuedHandler.php