[Process] Fixed inconsistent test

Sometimes the process no longer appears to be running when the signal is sent which causes a LogicException to be thrown.
This doesn't appear to be consistent and I can reproduce it randomly on my local machine. To avoid having tests fail at random
I decided that it's better to send the signal only if the process is still marked as running.

Tests/ErrorProcessInitiator.php

@@ -25,7 +25,7 @@
     while (!str_contains($process->getOutput(), 'ready')) {
         usleep(1000);
     }
-    $process->signal(\SIGSTOP);
+    $process->isRunning() && $process->signal(\SIGSTOP);
     $process->wait();
 
     return $process->getExitCode();