[13.x] Fix quietly() making throw() unreachable on process results

[xurshudyan]

Combining quietly() with throw() never produces a ProcessFailedException,
so the catch block below is dead code:

try {
    Process::quietly()->run('composer install')->throw();
} catch (ProcessFailedException $e) {
    $this->error("Install failed with code {$e->getCode()}");
}

PHP Fatal error: Uncaught Symfony\Component\Process\Exception\LogicException:
Output has been disabled.