ci/github-script: add gh dependency to dev shell

(cherry picked from commit cdd1931ace)

ci/github-script/README.md

@@ -5,8 +5,8 @@ It provides a `nix-shell` environment to run and test these actions locally.
 
 To run any of the scripts locally:
 
-- Provide `gh` on `PATH` and make sure it's authenticated.
 - Enter `nix-shell` in `./ci/github-script`.
+- Ensure `gh` is authenticated.
 
 ## Labeler
 

ci/github-script/shell.nix

@@ -5,12 +5,14 @@
 
 pkgs.callPackage (
   {
-    mkShell,
+    gh,
     importNpmLock,
+    mkShell,
     nodejs,
   }:
   mkShell {
     packages = [
+      gh
       importNpmLock.hooks.linkNodeModulesHook
       nodejs
     ];