Ensure fresh download of repoOverrides from git after update

I have the following override:

  nixpkgs.config.packageOverrides = pkgs: {
    nur = import (builtins.fetchTarball "https://github.com/nix-community/NUR/archive/master.tar.gz") {
      inherit pkgs;
      repoOverrides = {
        instantos = import (builtins.fetchGit {
          url = "https://github.com/ppenguin/instantNIX.git";
          ref = "change-instantdata-uc";
          rev = "112e7ef957dd7afff893ed1c4e8502829dcfae60";
        }) { inherit pkgs; };

but when I make a fresh commit to the repo and change the rev accordingly, a

sudo nixos-rebuild switch

does not always apply the corresponding changes (i.e. the repo is not re-evaluated/re-downloaded).

After I do sudo nix-collect-garbage, the above fetchTarball repo is apparently re-downloaded, but not the git repo.

How can I ensure that the git repo is always evaluated for updates?