msglist-diffing tests: Debug/fix a flake with stream-subscribed status changing

[chrisbobbe]

19 failures under

messages -> piece descriptors -> content HTML is stable/sensible › other interesting cases (single messages)

; here's one:

FAIL src/webview/__tests__/generateInboundEventEditSequence-test.js (9.761 s)
  ● messages -> piece descriptors -> content HTML is stable/sensible › other interesting cases (single messages) › message in unsubscribed stream
    expect(received).toMatchSnapshot()
    Snapshot name: `messages -> piece descriptors -> content HTML is stable/sensible other interesting cases (single messages) message in unsubscribed stream 1`
    - Snapshot  - 2
    + Received  + 2
    @@ -1,12 +1,12 @@
      <div class="msglist-element timerow" data-msg-id="-1">
        <div class="timerow-left"></div>
        Dec 31, 1969
        <div class="timerow-right"></div>
      </div><div class="msglist-element header-wrapper header stream-header topic-header" data-msg-id="-1" data-narrow="dG9waWM6MTpleGFtcGxlIHRvcGlj">
    -   <div class="header stream-text" style="color: black;
    +   <div class="header stream-text" style="color: white;
    -               background: hsl(0, 0%, 80%)" data-narrow="c3RyZWFtOjE=">
    +               background: #123456" data-narrow="c3RyZWFtOjE=">
          # stream 1
        </div>
        <div class="topic-text">example topic</div>
        <div class="topic-date">Dec 31, 1969</div>
      </div><div class="msglist-element message message-full" id="msg--1" data-msg-id="-1" data-mute-state="shown">
      286 |     );
      287 |
    > 288 |     expect(msglistElementsDiv.innerHTML).toMatchSnapshot();
          |                                          ^
      289 |   };
      290 |
      291 |   test('HOME_NARROW', () => {
      at check (src/webview/__tests__/generateInboundEventEditSequence-test.js:288:42)
      at Object.<anonymous> (src/webview/__tests__/generateInboundEventEditSequence-test.js:434:7)

That difference in rendering points to a stream being subscribed, when the snapshot expects it to be unsubscribed. Will send a PR shortly.