fix(http): use exclusive locks for file session writes (#1366)

Author: brendt

packages/http/src/Session/Managers/FileSessionManager.php

@@ -123,7 +123,7 @@ private function persist(SessionId $id, ?array $data = null): Session
             $session->data = $data;
         }
 
-        Filesystem\write_file($path, serialize($session));
+        Filesystem\write_file($path, serialize($session), LOCK_EX);
 
         return $session;
     }