feat!: Update action to node v16

This was required as github deprecates all node v12 actions:
https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/

Further node12 is no longer maintained: https://github.com/nodejs/release#release-schedule

Close #285

BREAKING CHANGE: Dropping support for node v12.

action.yml

@@ -42,7 +42,7 @@ inputs:
     required: false
     default: "latest"
 runs:
-  using: "node12"
+  using: "node16"
   main: "./dist/index.js"
 branding:
   icon: "book"