redirect stderr via descriptor spec

see php/php-src#13778 (comment)

Author: staabm

src/Util/PHP/AbstractPhpProcess.php

@@ -203,10 +203,6 @@ public function getCommand(array $settings, ?string $file = null): array
             $command[] = $this->arguments;
         }
 
-        if ($this->stderrRedirection) {
-            $command[] = '2>&1';
-        }
-
         return $command;
     }
 

src/Util/PHP/DefaultPhpProcess.php

@@ -94,6 +94,9 @@ protected function runProcess(string $job, array $settings): array
             1 => $handles[1] ?? ['pipe', 'w'],
             2 => $handles[2] ?? ['pipe', 'w'],
         ];
+        if ($this->stderrRedirection) {
+            $pipeSpec[2] = ['redirect', 1];
+        }
 
         $process = proc_open(
             $this->getCommand($settings, $this->tempFile),