[Console] Remove invalid ProcessHelper specified usage

[viviengaetan]

Since Symfony 6.0, the ProcessHelper have the $cmd argument from its two methods run() and mustRun() typed as array|Process source.

When you try to run as described in the documentation with a string, PHP will throw a TypeError

Fatal error: Uncaught TypeError: Symfony\Component\Console\Helper\ProcessHelper::run(): Argument #2 ($cmd) must be of type Symfony\Component\Process\Process|array, string given, called in /app/src/FooCommand.php on line 22 and defined in /app/vendor/symfony/console/Helper/ProcessHelper.php:35

Documentation is invalid since 6.0 up to the latest version.

[javiereguiluz]

Good catch Gaëtan! Thanks and congrats on your first Symfony Docs contribution 🎉