fix(ReplyWidget): handle update_signal as successful reply

Fixes a partition[1][2] between SpeechBubble._update_text(), called when
a reply has been downloaded from the Journalist API, and
ReplyWidget._on_reply_success(), called when a reply has been
successfully sent via the SDK.  In the case where the Client starts with
a reply still pending from a previous session and the reply is
subsequently downloaded, ReplyWidget.status will not be updated from
Reply.send_status unless it too listens for the SpeechBubble's
update_signal, and future calls to ReplyWidget._update_styles() will be
based on a stale ReplyWidget.status.

While conflating these signals is not ideal, in the current data model
we might as well, since a reply downloaded from the server is by
definition one that has been successfully sent to the server.  See
<#1493 (comment)>.

[1]: #1486 (review)
[2]: #1486 (comment)

securedrop_client/gui/widgets.py

@@ -2037,6 +2037,7 @@ def __init__(  # type: ignore [no-untyped-def]
 
         self.check_mark.show()
 
+        update_signal.connect(self._on_reply_success)
         message_succeeded_signal.connect(self._on_reply_success)
         message_failed_signal.connect(self._on_reply_failure)
         self.controller.update_authenticated_user.connect(self._on_update_authenticated_user)

tests/gui/test_widgets.py

@@ -4518,6 +4518,7 @@ def test_ReplyWidget_success_failure_slots(mocker):
     )
 
     # ensure we have connected the slots
+    mock_update_signal.connect.assert_called_with(widget._on_reply_success)
     mock_success_signal.connect.assert_called_once_with(widget._on_reply_success)
     mock_failure_signal.connect.assert_called_once_with(widget._on_reply_failure)
     assert mock_update_signal.connect.called  # to ensure no stale mocks