Document the de facto staging deployment procedure

We update both staging main and moduletest.

docs/runbooks/how-release-a-new-version-for-approval-testing.md

@@ -20,8 +20,9 @@ production library sites.
 1. In your local environment ensure that your checkout of the `main` branch for
    `dpl-platform` is up to date.
 2. Create a new branch from `main`.
-3. Open `infrastructure/environments/dplplat01/sites.yaml`, find `staging`,
-   then update the value of `dpl-cms-release` for `staging` to the new version
+3. Open `infrastructure/environments/dplplat01/sites.yaml`, find
+   `staging`, then update the value of `dpl-cms-release` and
+   `moduletest-dpl-cms-release` for `staging` to the new version
 4. Commit the change and push your branch to GitHub and create a pull request.
 5. Request a review for the change and wait for approval.
 6. Start `dplsh` from the `/infrastructure` directory of your local