Last task in workflow doesn't update to succeeded in graph GUI

[jfrost-mo]

Description

After a workflow reaches its final cycle point, and the last task completes, the reported state in the graph view of the GUI still claims the task to be running, when it is not.

Reproducible Example

Run a workflow, opening it in cylc gui on the graph view. Once the workflow reaches its final cycle point, and the last task completes, observe the reported state of that task on the graph. It will be left in a running state, despite actually having succeeded.

Expected Behaviour

The task in the GUI should be marked as succeeded.