replace hub with gh

ref: mislav/hub#3338 (comment)
ref: https://docs.github.com/ja/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally?tool=cli#modifying-an-active-pull-request-locally

.github/workflows/test-action.yml

@@ -27,7 +27,7 @@ jobs:
  PR_URL="${{ github.event.issue.pull_request.url }}"
  PR_NUM=${PR_URL##*/}
  echo "Checking out from PR #$PR_NUM based on URL: $PR_URL"
- hub pr checkout $PR_NUM
+ gh pr checkout $PR_NUM
 
  - name: Test Local Action
  id: test-action