action test [nfc]: Remove irrelevant issue reference

Coming up with a realistic test case doesn't actually require
invalidating API key. Because the goal is to use routes that exist in
the app (`InboxPageBody` has become a part of `HomePage` and
doesn't exist on its own), we can set up HomePage and MessageListPage
instead.

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

test/widgets/actions_test.dart

@@ -187,7 +187,7 @@ void main() {
 
       final pushedRoutes = <Route<dynamic>>[];
       testNavObserver.onPushed = (route, prevRoute) => pushedRoutes.add(route);
-      // TODO(#737): switch to a realistic setup:
+      // TODO: switch to a realistic setup:
       //   https://github.com/zulip/zulip-flutter/pull/1076#discussion_r1874124363
       final account1Route = MaterialAccountWidgetRoute(
         accountId: account1.id, page: const InboxPageBody());