msglist: Test fixture for MessageList should use an anchor from the set of faux messages

Author: sirpengi

test/widgets/message_list_test.dart

@@ -29,9 +29,8 @@ Future<void> setupMessageListPage(WidgetTester tester, {
   final List<StreamMessage> messages = List.generate(10, (index) {
     return eg.streamMessage(id: index);
   });
-  final message = eg.streamMessage();
   connection.prepare(json: GetMessagesResult(
-    anchor: message.id,
+    anchor: messages[0].id,
     foundNewest: true,
     foundOldest: true,
     foundAnchor: true,