Documentation shows old-style `rose stem` command

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

https://metoffice.github.io/lfric_apps/developer_guide/lfric_apps_rose_stem/index.html is referring to the older `rose stem` way of running tests, this should be updated to `cylc vip -z group= ./rose-stem`

### Further details of the issue.

_No response_

Open the developer guide page at https://metoffice.github.io/lfric_apps/developer_guide/lfric_apps_rose_stem/index.html and locate the outdated `rose stem` test command. Update it to the specified `cylc vip -z group= ./rose-stem` form, then verify the rendered documentation shows the new command.

Written by the indexing model from the issue text.