message: Fix test case
  The test case is:
  "mentions message when a single message was pinned, with multiple previously pinned messages"
  However, the test case was also unpinning messages. That is now fixed.
diff: @@ -67,7 +67,7 @@ describe('TextForEvent', () => {
  });
  it("mentions message when a single message was pinned, with multiple previously pinned messages", () => {
  - const event = mockPinnedEvent(['message-3'], ['message-1', 'message-2']);
  + const event = mockPinnedEvent(['message-1', 'message-2', 'message-3'], ['message-1', 'message-2']);
  const plainText = textForEvent(event);
  const component = renderer.create(textForEvent(event, true));
  