TMSS-849: import fix

SAS/TMSS/backend/services/tmss_postgres_listener/lib/tmss_postgres_listener.py

@@ -30,7 +30,6 @@ from lofar.common import dbcredentials
 from lofar.common.util import single_line_with_single_spaces
 from distutils.util import strtobool
 from datetime import datetime, timedelta
-from lofar.sas.tmss.tmss.tmssapp.models import Subtask
 
 
 class TMSSPGListener(PostgresListener):
@@ -204,6 +203,7 @@ class TMSSPGListener(PostgresListener):
            because their status is implicitly derived from their subtask(s)
            send both object.updated and status change events'''
         try:
+            from lofar.sas.tmss.tmss.tmssapp.models import Subtask
             subtask = Subtask.objects.get(id=subtask_id)
 
             # check if task is new or changed... If so, send event.