build: bundle file with .mjs extension

action.yml

@@ -34,4 +34,4 @@ outputs:
     value: ${{ steps.process-inputs.outputs.build-dir }}
 runs:
   using: node20
-  main: dist/index.js
+  main: dist/index.mjs

rollup.config.js

@@ -5,6 +5,7 @@ export default {
   input: "src/index.ts",
   output: {
     dir: "dist",
+    entryFileNames: "[name].mjs",
   },
   plugins: [nodeResolve(), typescript()],
 };