move UseThenDisconnect into queueworker

This makes the tests pass while maintaining the same behavior.

workers/queueworker.py

@@ -8,8 +8,11 @@ from datetime import datetime, timedelta
 from threading import Thread
 from time import sleep
 
+from app import app
+
 from data.model import db
 from data.queue import WorkQueue
+from data.database import UseThenDisconnect
 
 from workers.worker import Worker
 
@@ -123,7 +126,8 @@ class QueueWorker(Worker):
       logger.debug('No more work.')
 
   def update_queue_metrics(self):
-    self._queue.update_metrics()
+    with UseThenDisconnect(app.config):
+      self._queue.update_metrics()
 
   def mark_current_incomplete(self, restore_retry=False):
     with self._current_item_lock: