use latest for grafana-station-dashboards instead of image tag in this repo

infra/grafana-lofar-central.levant.nomad

@@ -68,7 +68,7 @@ job "grafana" {
         policies = ["default"]
       }
       config {
-        image       = "git.astron.nl:5000/lofar2.0/grafana-station-dashboards:[[.image_tag]]"
+        image       = "git.astron.nl:5000/lofar2.0/grafana-station-dashboards:latest"
         mount {
           type   = "bind"
           source = "local/datasources/"