fix: revert CronWorkflow schedules back to schedule field

The schedules array field requires Argo Workflows v3.6+ and breaks
older installations. Keep the singular schedule field which is
supported across all versions.

Author: Nissan Pow

metaflow/plugins/argo/argo_client.py

@@ -325,7 +325,7 @@ def schedule_workflow_template(self, name, schedule=None, timezone=None):
             "metadata": {"name": name},
             "spec": {
                 "suspend": schedule is None,
-                "schedules": [schedule] if schedule is not None else [],
+                "schedule": schedule,
                 "timezone": timezone,
                 "failedJobsHistoryLimit": 10000,  # default is unfortunately 1
                 "successfulJobsHistoryLimit": 10000,  # default is unfortunately 3