Checkout pull request HEAD commit

Author: dentarg

action.yml

@@ -25,6 +25,7 @@ runs:
   steps:
     - uses: actions/checkout@v4
       with:
+        ref: ${{ github.event.pull_request.head.sha }} # https://github.com/actions/checkout#checkout-pull-request-head-commit-instead-of-merge-commit
         fetch-depth: 2 # https://github.com/actions/checkout#checkout-head
 
     - uses: ruby/setup-ruby@v1