chore: migrate to esm (#334)

* chore: update unit tests

* fix: follow latest action template

* chore: add licenses and workflows

* chore: remove bloat

* chore: fix linter

src/index.ts

@@ -0,0 +1,8 @@
+/**
+ * The entrypoint for the action. This file simply imports and runs the action's
+ * main logic.
+ */
+import { run } from './main.js'
+
+/* istanbul ignore next */
+run()