Add dummy job to guestfs_index workflow so that its status isn't marked as failing

[mawillcockson]

Currently, there are two errors:

• The workflow is marked as failing because no jobs are being run
• No jobs are being run even though they should be

The first one is fixed by adding a dummy job that always runs.

The second one is because the conditional isn't triggering, and can be introspected with some print debugging added in the dummy job.