minor #5797 [Process] use ProcessFailedException instead of RuntimeException. (aitboudad)

This PR was merged into the 2.7 branch.

Discussion
----------

[Process] use ProcessFailedException instead of RuntimeException.

| Q             | A
| ------------- | ---
| Doc fix?        | yes
| New docs?   | no
| Applies to     | all
| Fixed tickets | symfony/symfony#16269

Commits
-------

16ef37f [Process] use ProcessFailedException instead of RuntimeException.

Author: xabbuh

components/process.rst

@@ -24,13 +24,14 @@ The :class:`Symfony\\Component\\Process\\Process` class allows you to execute
 a command in a sub-process::
 
     use Symfony\Component\Process\Process;
+    use Symfony\Component\Process\Exception\ProcessFailedException;
 
     $process = new Process('ls -lsa');
     $process->run();
 
     // executes after the command finishes
     if (!$process->isSuccessful()) {
-        throw new \RuntimeException($process->getErrorOutput());
+        throw new ProcessFailedException($process);
     }
 
     echo $process->getOutput();