Update Node runtime version (#19)

Node.js 16 actions are deprecated.
Refs: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

action.yml

@@ -35,7 +35,7 @@ outputs:
     description: The token of the GitHub App on the current repository.
 
 runs:
-  using: node16
+  using: node20
   main: dist/index.js
   post: dist/index.js