When pulling screen with RefreshIndicator, the top stickerGroupSeparator should be pulled also

[minhdanh]

Hi, first thank you for your great package. I'm using it with the following settings:

RefreshIndicator(
      backgroundColor: Theme.of(context).colorScheme.primary,
      color: Theme.of(context).colorScheme.onPrimary,
      onRefresh: () {
        // BlocProvider.of<HomeStatsBloc>(context).add(LoadHomeStatsEvent());
        return Future.delayed(const Duration(seconds: 1));
      },
      child: GroupedListView<Transaction, String>(
        // TODO: this should bounce with the group header also
        // may need to ask grouped_list developer to fix
        physics: const BouncingScrollPhysics(parent: AlwaysScrollableScrollPhysics()),
        controller: _scrollController,
        useStickyGroupSeparators: true,
        ...

When I don't set useStickyGroupSeparators (meaning its value is false), I can pull the whole screen. But when that field is true, the top group separator won't be pulled, which makes it look odd to me. Here's how it looks:

Is there anyway I can still use useStickyGroupSeparators: true while also be able to pull the whole screen? Willing to create a PR for this if needed.