Mark DigestWorker and PushNotificationsWorker as nocoverage.

These two classes are tricky to test, and nocoverage-ing them
allows us to mark queue_processors.py as fully covered. We
still want to cover these two workers at some point, but for
now, it's nice to enforce full coverage for any future changes
to queue_processors.py.

Fixes (sort of) #6542.

tools/test-backend

@@ -37,6 +37,7 @@ target_fully_covered = {path for target in [
     # Once we have a nice negative tests system, we can add these:
     # 'zerver/webhooks/*/*.py',
     # 'zerver/webhooks/*/*/*.py',
+    'zerver/worker/queue_processor.py',
 ] for path in glob.glob(target)}
 
 not_yet_fully_covered = {

zerver/worker/queue_processors.py

@@ -322,7 +322,7 @@ class MissedMessageSendingWorker(EmailSendingWorker):  # nocoverage
     pass
 
 @assign_queue('missedmessage_mobile_notifications')
-class PushNotificationsWorker(QueueProcessingWorker):
+class PushNotificationsWorker(QueueProcessingWorker):  # nocoverage
     def consume(self, data):
         # type: (Mapping[str, Any]) -> None
         handle_push_notification(data['user_profile_id'], data)
@@ -430,7 +430,7 @@ class MessageSenderWorker(QueueProcessingWorker):
                            respond_send_message)
 
 @assign_queue('digest_emails')
-class DigestWorker(QueueProcessingWorker):
+class DigestWorker(QueueProcessingWorker):  # nocoverage
     # Who gets a digest is entirely determined by the enqueue_digest_emails
     # management command, not here.
     def consume(self, event):