minor edit to deploy preview action

Author: trevorcampbell

.github/workflows/deploy_pr_preview.yml

@@ -47,3 +47,4 @@ jobs:
               Hello! I've built a preview of your PR so that you can compare it to the current `main` branch.
               * PR deploy preview available [here](https://python.datasciencebook.ca/pull${{ github.event.number }}/index.html)
               * Current `main` deploy preview available [here](https://python.datasciencebook.ca/dev/index.html)
+              * Public production build available [here](https://python.datasciencebook.ca)