foot: add `passthru.updateScript`

updates foot itself and subpackage

pkgs/by-name/fo/foot/package.nix

···
     "themes"
   ];
 
+  passthru = { inherit stimulusGenerator; };
+  passthru.updateScript = ./update.sh;
+
   passthru.tests = {
     clang-default-compilation = foot.override {
       inherit (llvmPackages) stdenv;

pkgs/by-name/fo/foot/update.sh

···
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash
+#!nix-shell -p nix-update
+
+nix-update foot
+nix-update --version=skip foot.stimulusGenerator