Add more clarity around code-block in Dev UI Docs

[phillip-kruger]

As discussed in quarkiverse/quarkus-bon-jova-rockstar#164

[quarkus-bot]

Status for workflow Quarkus Documentation CI

This is the status report for running Quarkus Documentation CI on commit 852dd85.

✅ The latest workflow run for the pull request has completed successfully.

It should be safe to merge provided you have a look at the other checks in the summary.

[github-actions]

🙈 The PR is closed and the preview is expired.

[holly-cummins]

Approving, because these changes look good, and should be merged - but they might be incomplete, since I found the dev UI pages with a code block went blank on moving to 3.9.1, and these changes weren't enough to fix it. It looks like @phillip-kruger can't reproduce, though, so we will have to figure out what the issue is and if it's strictly local or could affect other users/extensions.

[holly-cummins]

I confirm the issue I was seeing was user error (thanks, @phillip-kruger!), so this is good to go.