fix path whitespace edge case

if the file has a space in the path, the command would not account for that and generate an invalid invocation. for example if the path was
/home/hans henrik/wrench/tests/Test/ServerTestHelper.php
the command would previously fail.

tests/Test/ServerTestHelper.php

@@ -134,6 +134,6 @@ public static function getNextPort(): int
      */
     private function getCommand(): string
     {
-        return \sprintf('/usr/bin/env php %s/server.php %d', __DIR__, $this->port);
+        return \sprintf('/usr/bin/env php ' . escapeshellarg(__DIR__ . '/server.php') . ' %d', $this->port);
     }
 }