with-post-step: use Node.js 16 instead of Node.js 12

https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/

with-post-step/action.yml

@@ -37,6 +37,6 @@ inputs:
     default: POST
 
 runs:
-  using: 'node12'
+  using: 'node16'
   main: 'main.js'
   post: 'main.js'