Fix run-tests.php hanging when a worker process dies without notice (#9931)

run-tests.php with `-jN` can hang if a parallel worker dies without notice. This
can happen due to fatal errors in the worker, or if the worker is killed.

- run-tests.php (main process)
  \_ run-tests.php (worker #0) // main process hangs if this one crashes
     \_ test-001.php (test-001.phpt)

Author: arnaud-lb

run-tests.php

@@ -1583,6 +1583,10 @@ function run_all_tests_parallel(array $test_files, array $env, $redir_tested): v
                     kill_children($workerProcs);
                     error("Could not find worker stdout in array of worker stdouts, THIS SHOULD NOT HAPPEN.");
                 }
+                if (feof($workerSock)) {
+                    kill_children($workerProcs);
+                    error("Worker $i died unexpectedly");
+                }
                 while (false !== ($rawMessage = fgets($workerSock))) {
                     // work around fgets truncating things
                     if (($rawMessageBuffers[$i] ?? '') !== '') {