[MINOR][CONNECT] Convert metadata to list to prevent silent metadata loss on retry/reattach - #58210

Unable to detect the workflow run for testing the changes in your PR.

1. If you did not enable GitHub Actions in your forked repository, please enable it by clicking the button as shown in the image below. See also Managing Github Actions Settings for a repository for more details.
2. It is possible your branch is based on the old master branch in Apache Spark, please sync your branch to the latest master branch. For example as below:

   git fetch upstream
   git rebase upstream/master
   git push origin YOUR_BRANCH --force