message: fix: don't overwrite the transaction on an event if it's already been set.
diff: @@ -203,7 +203,7 @@ export function parseRequest(
  };
  }
  - if (options.transaction) {
  + if (options.transaction && !event.transaction) {
  const transaction = extractTransaction(req, options.transaction);
  if (transaction) {
  event.transaction = transaction;
  