push-notifications: Update strings for private messages.

Updates strings with "private message" in push notifications to
use "direct message" instead.

zerver/lib/push_notifications.py

@@ -661,12 +661,12 @@ def get_gcm_alert(
         message.recipient.type == Recipient.HUDDLE
         and trigger == NotificationTriggers.PRIVATE_MESSAGE
     ):
-        return f"New private group message from {sender_str}"
+        return f"New direct group message from {sender_str}"
     elif (
         message.recipient.type == Recipient.PERSONAL
         and trigger == NotificationTriggers.PRIVATE_MESSAGE
     ):
-        return f"New private message from {sender_str}"
+        return f"New direct message from {sender_str}"
     elif message.is_stream_message() and trigger == NotificationTriggers.MENTION:
         if mentioned_user_group_name is None:
             return f"{sender_str} mentioned you in #{display_recipient}"

zerver/tests/test_push_notifications.py

@@ -2070,7 +2070,7 @@ class TestGetGCMPayload(PushNotificationTest):
             {
                 "user_id": hamlet.id,
                 "event": "message",
-                "alert": "New private message from King Hamlet",
+                "alert": "New direct message from King Hamlet",
                 "zulip_message_id": message.id,
                 "time": datetime_to_timestamp(message.date_sent),
                 "content": message.content,